Note: Because of the way I learned to play, I always use Assault, Sniper, Freeze, as my chosen weapons, especially for Insane difficulty. It is ok to try something different, try out the various towers and combinations to find what suits you. Everyone plays differently.

I got a lot of info from this Sanctum Wiki[sanctum-series.fandom.com], so thank you to whoever made it!

Several of the Maps for Insane come from or are inspired by rarestMeow's guide, check his guide out here :
https://steamproxy.net/sharedfiles/filedetails/?id=2218394198
He prefers the Tesla, so most of our strategy differs, but some overlap occurs.

When I first started playing, I watched a lot of cthrivevideo's Insane runs. Some of them were pretty difficult to do, especially since most of his vids predate when they added the Accelerator and other towers to the Tower list. But I learned a lot, and some of the Mazes come from cthrive. The Sanctum Wiki also has some of his stuff.

Section for Beginners:
1. Start on Easy or Normal. Get a feel for the game, the weapons, and how things work.
2. Focus on building a little of your maze first, maxing the time for the aliens to run through. The mazes I used for Insane can be used, and are available under their appropriate section.
3. Learn what towers go best against what enemy, the Enemies and/or Towers section of this guide can help with that. Place 1-3 of the appropriate Tower in your maze.
4. During the Building Phase, you can prepare for the current and upcoming alien waves by looking at the menu and clicking on the Wave list.
5. Where applicable, practice running backward through your chosen maze, that way you can stay in front of the Lumes, where you will be able to fire into their weakspot.

Tips:

• Where applicable, practice running backward through your chosen maze on lower difficulties, that way you are comfortable with it by the time you make it to Insane. Some maps, like Complex, you will be standing behind a Holo 95% of the time, so it depends on the map.
  
• For the "Survive all the waves..." Insane achievements, you do not have to 100% the core. It is possible, I have done it for many of them, but some are, well, insane lol. But the goal is just to survive for those.
  
• Effective weapons swapping is a skill that should be practiced a lot, since waiting on any weapon cooldown is effectively lost damage. Get used to swapping with Q and E, or your preferred keys.
  
• Weapon accuracy, especially with the Sniper, is also very important on Insane. Practice hitting weakspots.
  
• On some Insane Maps, in singleplayer, you will be doing most of the work yourself.

As mentioned in the General Tips, I favor the Assault, Sniper, and Freeze combo. So I will admit, I am a little bias about them lol.

Cost for all weapons :

Assault


Notes: A good rounded weapon. Primary fire is great for dealing lots of damage very quickly, especially against Soakers and Blockers. When paired with the Primary Fire of Freeze to clump enemies together, the Secondary Fire can obliterate large groups of Runners and Walkers easily.
It does overheat easily when firing the primary, so letting off the trigger for a sec/half-sec can help.
After firing one grenade, wait for a half-sec for the % to fall below 50%. This will give you the ability to fire a third grenade before the gun overheats. Thankfully, its cooldown is fairly fast, and it takes longer to overheat it the higher its Level is.
It is a close range weapon, so after a certain distance from an enemy, it won't hit at all. That distance does increase with leveling, but I am not sure how much.

Freeze


Notes: Slow is great for clumping enemies together for your Assault grenades or REX. I mainly use slow to allow myself and my towers more time to kill the Lumes. Paired with Slowfields, enemies will crawl through your maze. I mainly use Freeze to hold enemies in place either in front of a Holo, or as a last resort before they enter the Core. I generally don't fire Freeze unless i really need to, as it has a really long cooldown.
You can also use Slow to separate out enemies that are too clumped together, like Soakers, to allow you and your towers to hit them.

Sniper


Notes: Honestly my favorite weapon. Its good against every single enemy except for Runners. Has a fairly fast cool down, and on higher levels, you can solo waves with this gun. Its only downside is you need to really accurate with your shots on Insane. Missing even one shot can be what breaks a perfect run. Practicing with the Sniper on easier Difficulties against the various Lumes is highly recommended. Get a feel for how they move, their speed, and good timing.
I am not perfect, but I am fairly good, as I have 100% several maps on Insane by myself. Some with much Reloading of checkpoints, swearing, and frustration, but oh that sweet sweet satisfaction of victory *chef's kiss*
Combine the Sniper with Holos and Slow and its just OP. Love this gun.

Part 2 because apparently there is a character limit on sections. Fun fun.

Cost for all weapons :

REX


Notes: This is a fun gun, and on higher levels, does a LOT of damage. My main issue with it is its really long cooldown time. Also, the REX never hits an enemy's weak spot, even if aimed directly at it. So while the damage is high, those two downsides are why I don't use it, unless I am just goofing around.

Shotgun


Notes: From the Wiki :
The Shotgun is a close-range weapon that fires multiple pellets at once with a relatively high spread. Its secondary fire unloads multiple shells at once. Each shell contains eight pellets, which spread randomly when shot. The primary fire rate is approximately 1.1 shots per second, and the secondary fire loads one shell every second.
I like the Shotgun, at close range, its a beast. But the slow fire rate is what what breaks it for me. That, on top of it being hard to use it to its full potential unless you are really close range.

Tesla


Notes: From the Wiki :
The Tesla's damage output on a single target is weaker than the Assault Gun's primary fire, but the Tesla's primary fire affects a small area. This makes it effective against tightly packed groups such as Runners, especially in conjunction with a Slow Field or a Freeze Gun.
The Tesla's secondary fire bounces to up to two nearby enemies, so it is most effective against clusters of three or more enemies. The Freeze Gun is recommended to cluster enemies together. The Tesla's secondary fire is also somewhat effective against flying enemies.
When playing around with it, I noticed that the Primary Fire did not penetrate a Tanks shield, even while aiming at the weak spot.
The Tesla is a good alternative to the Assault, but the lesser damage is why I choose the Assault.

A lot of the general info and basic strategy I am getting from the Sanctum Wiki[sanctum-series.fandom.com]

Walker
Info:
The Walker is a creature that lacks any special abilities,they are very easy to kill, but comes in large numbers. It has a tendency to clump together, so explosives are generally very effective against the Walker.
Strategies:
Clumping the wave together in a group using Slow, using the Sniper on weakpoints to thin the ranks, and then using Assault Grenades to reduce health/kill many at once is the best way to kill them.
On higher levels and waves, slowing them down becomes necessary, so you have more time to Snipe and Grenade them, and your towers help.
Gatlings are most effective in dealing lots of damage really quickly to waves of Walkers.
Scatter Lasers are good, as they can hit both air and ground, but deal less damage than Gatlings.
I don't use them, but Mortar is also effective, but only when paired with Slowfields and Freeze Gun.

Charger
Info:
The Charger accelerates to incredible speeds on long straight paths, but slows down significantly when they turn. A maze with many twists and turns is therefore an effective counter.
Strategies:
Gatlings and Lightnings will deal good damage if placed well, especially if they are placed in a position which has the Chargers walking slowly around them. The Scatter Laser is very powerful against Chargers since it can fire over walls and most mazes include a large number of turns to slow chargers down.
These guys are one of the banes of my existence on maps without a lot of curves, or ones like Christmas where the path is set. A high level Assault will chew through them, and Sniper is good for thinning the waves. Slow is more effective the more curves in your maze, slowing them to a crawl, but not as effective if they are allowed to get up to speed.
Definitely avoid being in front of them if they are running, cause they will LAUNCH you, wasting time.

Soaker
Info:
The Soaker is a durable creature that incurs more damage with every hit it takes, making rapid fire weapons the most effective against them. One of the more difficult and frustrating enemies of the game.
Strategies:
On higher levels, these can take forever to pop.
On the players part, one of the best strategies is to :
Slow, Fire Assault Primary until about 20-25%, Empty Sniper clip, repeat.
For Towers, Gatlings at the beginning of the maze to pour on the damage, and Lightnings at the end to help pop. Scatter Laser is also helpful for its high fire rate. An optimally placed Accelerator paired with Slowfields and Slow/Freeze can kill off Soakers, but usually only one, maybe two.

Big Walker
Info:
The Big Walker, like the smaller Walker, does not have any special abilities. It is large and durable and thus can be difficult to kill, but not many appear in a wave.
Strategies:
Their main problem is high health. Lightning towers do a lot of damage to these guys, but really, any tower is effective a whittling them down. Like with the Soaker, the player should Slow, Snipe the weakspot, and then use Assault until the Slow is done with its cooldown, then repeat. On Insane, it is especially important to hit that weakspot as much as possible with the Sniper, and if you can pair it with a Holo, even better.

Runner
Info:
The Runner is a very small, weak and fast enemy that comes in large groups. Because of its size and speed, it may often slip past the player, possibly unnoticed. It also escapes the range of attacking towers quite fast.
Strategies:
One of the easiest enemies, but also one of the easiest to miss one and it ends up running into your Core. Towers with a high rate of fire like Gatling and Scatter are most effective. One of the best ways to kill them, is to Slow the group so they bunch up, and then lob Assault Grenades into them. On higher levels, it is essential to do this, to reduce their health enough to kill them off.

Blocker
Info:
The Blocker is a creature that can temporarily curl up into an immovable ball to negate 50% of damage inflicted upon it. Weapons that can inflict a high amount of damage per shot are most effective against it, as the Blocker curls up shortly after taking damage from players. The Blocker is a high-priority target at the beginning of the wave; if it is left alone it will speed through the maze. The player should keep them in check and make them curl up at the right places in the maze.
Strategies:
Thankfully, there are never too many of these, and as long as you keep them in check, they are easy to kill. Most towers are effective against them, as them will reduce their overall health, but the best strategy is to shoot them where they will curl up in front of some Lightnings or an Accelerator. Using Slow on them will also help keep them pinned for longer.
Sniper is very effective against them, sometimes killing them after one or two shots. Pair with a Holo and they are easy to deal with.

Tank
Info:
The Tank has very thick armor that reduces incoming damage by a set amount for each hit when its body is glowing blue. While armor shield is active: damage reduction per hit = current wave number × 5.
Strategies:
Violator and Lightning are very effective against Tanks. Most other towers are not. An optimally placed Accelerator paired with Slowfields and Slow/Freeze can kill off Tanks, but usually only one, maybe two. Snipe-Slow-Grenade-Repeat is the most effective strategy on the players part. Also, dealing enough damage to make the Tank lower its shield will allow even Gatlings and Scatters to damage them. Pair the Sniper with Holos to maximize damage.

Hoverer
Info:
The Hoverer has a shield on its anterior side that makes it immune to damage from the front. It is only vulnerable in the back, so they must be shot from behind.
Strategies:
Lightnings, Scatter Lasers, and Gatlings all do fairly well against Hoverers. A maze that forces them to turn its back to the turrets is most effective. These guys are tough to deal with most of the time, setting up your maze so you have at least one place where you can Snipe them from behind through a Holo is very effective. Slowing them down so you have enough time to kill them is very important, because these guys make it through the maze fairly quickly.

A lot of the general info and basic strategy I am getting from the Sanctum Wiki[sanctum-series.fandom.com]

Bobble Head
Info:
The Bobble Head is completely immune to damage on the body, and only its head is vulnerable to damage. It swings its head from side to side as it walks, making it a challenge to hit.
Strategies:
Honestly, it's one of my favorite enemies. Low health and low wave numbers make for a very easy time, you just need to be accurate with the Sniper. Slow and Slowfields are also your friend here to make it easier to hit them. Towers are basically useless against them, so using the Sniper or the Assault at close range is one of the only ways to kill them.
Because Towers can't hurt or kill them, you should take them out quickly to free up your Towers to aim at other enemies.

Spitter
Info:
As the Spitter walks, it occasionally spits out a parasite that scans its surroundings for living threats to the Spitter. If one is found, the parasite will chase it and explode when it reaches its target or gets shot. The Spitter's weak spot is the sac of goo on its back, which fills up before it spits and empties again. It is possible that more damage is done to the weak spot as it fills up, with the maximum damage inflicted just before it spits.
The Spitter is exclusive to the maps found in Map Pack 2.
Strategies:
Hated these things, very annoying. They are fast, and if not controlled, will make you waste too much time. Hitting their weakspot with the Sniper is the best way to deal with them. Assault is also effective, but not as much. Their spit attack is very annoying, as it will launch you a little bit and disrupt shots. It is similar to getting Tackled. The Spit is like a heat seeking missile, it will follow you. Thankfully, shooting it with any weapon except the Freeze Gun will destroy it. Best strategy is to Snipe them, Slow them, use the Assault to destroy the spit and do some damage, then repeat.

Dodger
Info:
The Dodger is a small flying creature that moves erratically.
Strategies:
Anti-Air, Violator, and Scatter are all effective towers against Dodgers. They are easy to kill, if you can hit them. Best bet is to hit them with the Sniper just after they have moved, so you won't miss if they jump in the middle of the shot. On higher levels, it is easy to accidentally let some get by your towers while you are focusing on ground units. Make sure to thin their numbers with the Sniper, or have your Towers properly upgraded to deal with them. If they are close enough, you can hit them with the Assault, but you usually need to be higher up to do so.

Spore Pod
Info:
The Spore Pod is a slow flying creature that typically attacks in swarms that fill up the sky.
Strategies:
Anti-Air towers are the best because of its splash damage and the Spore Pods' tendency to cluster together. Scatter Laser towers are less effective against individual Spore Pods, but in large numbers they are effective because their hitscan attack and rapid fire rate reduce overkill and the number of shots wasted on dead Spore Pods.
The Sniper rifle is by far the best weapon because of the Spore Pod's slow speed and large weak spot. Whenever convenient, target the stragglers to increase the effectiveness of the Anti-Air towers' splash.
If your Sniper kills them in one shot, then have at it. If it only damages them, Snipe to damage only. Since reducing their health will help maximize splash damage from the Anti-Air Towers.

Glider
Info:
The Glider is a fast flying creature. Its speed can pose a problem to Anti-Air towers as their rockets are often too slow to keep up with it, but the Glider has relatively low health.
Strategies:
Scatter Lasers are effective when not swamped by ground targets because of their long range and hitscan attack, and the low health of the Glider.
Anti-Air towers in large numbers perform reasonably well because each rocket fired towards a Glider has a chance to hit it.
Violators are very effective, as long as you can keep them from targeting ground units.
Use the Sniper to hit the glowing weak spot on their heads, and take them down quickly. The wings are easier to shoot, but will not provide critical damage.
Be careful on higher levels, cause these will fly past your towers really quickly. On some Insane maps, you have to kill these yourself a lot of the time.

Israphel
Info:
Israphel is the special final boss on the Yogscave map. He is, essentially, a super powered Spitter. The monster wave list has no information on him. He shoots projectiles at players and has a weakspot on his back, just like a normal Spitter.
He is inspired by Israphel, the main antagonist of the Yogscast's "Shadow of Israphel" series.
Strategies:
Hated this guy. I lost so many times before I figured out an effective strategy. See the end of the Yogscave/Below section in my Insane Maps Guide.

A lot of the general info and basic strategy I am getting from the Sanctum Wiki[sanctum-series.fandom.com]
All of the cost info and other info is mentioned there. I can put that info here if someone asks me to, but the table formatting to make it look neat and clear takes up a lot of space in the editor.
Usage ranks:
Never use - E -> D -> C -> B -> A - Always use

Block Towers and Televators
Your basic components of a Maze.
Try to have a few carefully placed Televators, the less resources you spend on them the better.

Gatling[sanctum-series.fandom.com]
Rank: B
Info:
The High Velocity Metal Dispenser Gatling tower sprays ground enemies with high-caliber rounds at great speed. Because of its rate of fire, its accuracy is poor, so it is best used at short distances.
Enemies : Ground
Strategies:
This tower is best used at the beginning of a Maze to help thin large waves of Walkers, Runners and Chargers. It is great at ramping up damage on Soakers, and can even hit a Hoverer if its back is to the Tower. They are unable to penetrate the Shield of a Tank, but can do damage if the player or another tower breaks the Shield.
It will fire at whatever target is nearest, but like the Assault, it has a wide spread, so not all shots will land. The closer the target, the better the DPS.
Its line of sight can be obstructed by other blocks and towers, so its best to have a bunch of Gatlings grouped together to allow better line of sight.
The space between adjacent Gatlings can serve as a ground level passage for the player, but not for enemies. This can be used to create ground-level shortcuts for navigation between maze trenches.

Lightning[sanctum-series.fandom.com]
Rank: B
Info:
The Lightning tower sends bolts of electric discharge at the enemies. Every shot is very powerful, but the tower's rate of fire is slow.
After sufficient upgrades, the Lightning tower's bolts bounce between targets. At level 3 each bolt bounces once, and at level 5, twice. The damage is reduced by 50% for each bounce, so a level 6 Lightning tower can inflict up to 3500 × (1 + 0.5 + 0.25) = 6125 damage per shot.
Enemies : Ground
Strategies:
These are your heavy hitting towers outside of the Violator. These are most effective against enemies that have a lot of health and are slow. Use against Tanks, Hoverers, Big Walkers, and to pop Soakers.
Other than the bounce, they only hit one enemy per shot, and it has a slow fire rate, so the best place to put them is around a curve, or where enemies will run by them twice. Pair with slowfields to allow them time to fire several shots at one enemy.

Scatter Laser[sanctum-series.fandom.com]
Rank: A
Info:
The R4-ND-OM Scatter Laser fires high-powered beams at enemies. As a side effect of having to channel such high-powered energies, the targeting system may be a little erratic; unlike other towers, the Scatter Laser randomly fires at enemy within its range.
The Scatter Laser has perfect accuracy, but randomly fires at any enemy within its range.
Enemies : Ground and Air
Strategies:
The main strength of the Scatter Laser is its ability to shoot both air and ground units. This can also be its weakness, however, as the towers do not always attack what you want them to attack.
These are good towers to use to supplement Anti-Air towers, as they can help reduce health and take out stragglers. They also have a wider range on higher levels.
They are also good because they can shoot over the Maze, unlike the Gatlings.
I mainly use them to help control waves, as they work against almost any enemy.

Slow Field[sanctum-series.fandom.com]
Rank: A
Info:
The Synthetic Lifeform-Oscillation Warp Field, commonly known as the Slow Field, slows down any player or ground creature that enters its boundary. It affects everything: running speed, animation, jump duration, rate of fire, and weapon cooldown. Enemies are also slightly tinted while in a Slow Field, similar to when affected by the Freeze Gun.
The slowing effect stacks with the Freeze Gun's primary fire.
Enemies : Ground
Strategies:
1. buying time: building level 1 Slow Fields along the entire path, causing the enemies to need 25% more time to pass through. This, in effect, lengthens your maze by 25% without spending a lot of money.
2. maximizing a killbox: building higher-level Slow Fields in an area that is saturated with upgraded towers, thus maximizing the effect of these towers
3. clumping: use slow fields to clump enemies to maximize area of effect attacks, such as from mortars, the tesla rifle, the assault rife's grenade, or the Rex.
Why not all three lol. When the map allows it, I generally use all three methods to take out the enemies. Utilize Slowfields with a Holo and your weapons, and its a fun time.
I favor these over Ampfields, because the hit window is really small for an Ampfield, so unless you are stationary and ready to fire when the Lumes pass over an Ampfield, the potential is wasted.

Anti-Air[sanctum-series.fandom.com]
Rank: A
Info:
The Double Twin-Linked Anti-Air turret launches target seeking missiles that damages any flying enemies caught in the explosion. It is very effective against closely packed flying enemies.
Enemies : Air
Strategies:
Due to the low fire rate and high range of AA towers, a few powerful towers are better than many weak ones.
The AA tower's homing missile will (presently) not lock onto a new target if it's original target dies mid-flight. Consequently, it is advised to place AA towers far apart so they will not lock onto the same target.
Having multiple lines of AA towers will maximize their efficiency. Two in the front, two in the middle, and two in the back would allow for the first set to weaken the target, the second set to kill it, with the 3rd there to ensure the death of any stragglers.
Air units tend to go along the outskirts of your maze, instead of the middle. As such, placing an AA tower against either wall is more effective than two AA towers a block apart in the middle.
These are your main defense against the three types of Air Lumes. Upgrade towers so the shots are fast enough to catch Gliders and you are set. Make sure you thin the ranks with your Sniper on higher difficulties and waves.
When you don't need them anymore towards the end of some Maps, you can sell them to regain a few resources.

Holo[sanctum-series.fandom.com]
Rank: A
Info:
The Holo tower multiplies the damage of hitscan shots and projectiles -- including those of towers -- that pass through it. Multiple Holo towers can be aligned in order to amplify one shot multiple times, but the damage increase of each successive Holo diminishes significantly.
See the Wiki for the Math behind the Holo damage and reduction as shots pass through several.
TL;DR : shooting through a max of two lvl 6 Holos is the most cost/damage efficient, you can stack a third lvl 6, but it only increases the damage another 30-40%.
Enemies : Ground and Air
Strategies:
Use them in key places in your Maze. Most of the time, this is in the beginning, where you can shoot into the spawn point. On higher difficulties and waves, it is necessary to have that amplified damage from your weapons to kill off the waves.

A lot of the general info and basic strategy I am getting from the Sanctum Wiki[sanctum-series.fandom.com]
All of the cost info and other info is mentioned there. I can put that info here if someone asks me to, but the table formatting to make it look neat and clear takes up a lot of space in the editor.
Usage ranks:
Never use - E -> D -> C -> B -> A - Always use

Note : This second section contains a lot of towers that I don't use, and know almost nothing about, so their strategy sections will be sparse. If anyone has used them effectively even on Insane levels, let me know, and I will add your info to the guide and list you as the contributor.

Violator[sanctum-series.fandom.com]
Rank: C
Info:
The Violator is a very high-damage, long-range, slow-firing, turret that attacks ground and air enemies.
Strategies:
Because its attack is hitscan and accuracy, the Violator is effective against even the fastest enemies. It aims at the center of its target, and as such is not reliable against enemies with small weak spots.
This also means Tanks. So if the damage is high enough, it will break the shield, but if not, it will just hit their center mass and be blocked if the shield is still up.
They are great against all Air units, and are fast enough to hit Gliders, but have a slow Fire Rate, so some might slip by before it has a chance to recharge. If you pair these with Anti-Air it is a great combo.
One of the main faults of a Violator is they will target one unit, and wont switch targets until that unit is dead or out of range. This is a problem if it targets a Hoverer that never exposes its back or a Bobble Head that it cannot hit.

Accelerator[sanctum-series.fandom.com]
Rank: A
Info:
The Accelerator is a tower whose rate of fire is proportional to the amount of time for which it has been locked onto its current target.
The Accelerator gets a 25% fire rate increase for each shot at the same target. When it switches targets, the fire rate bonus is lost.
Strategies:
The Accelerator is most effective at the cusp of a U-turn in the maze because there it can sustain fire upon a single target for the longest amount of time. Its increasing rate of fire makes it especially useful against slow enemies such as Hoverers, Soakers and Tanks, but suffers against fast targets such as Runners and Walkers.
Slow Fields built around the Accelerator are more beneficial to it than to other towers. An Amp Field may be placed at the end of the Accelerator's range so that players can freeze enemies on it when the Accelerator has been locked on them for a long time.
I'll be honest, I didn't use these in most of my runs. I only recently discovered just how OP they were if you can put them in just the right spot and surround their range of fire with Slowfields.
But they are really good, I used them in Chasm and in Yogscave against Israphel.

Mortar[sanctum-series.fandom.com]
Rank: E
Info:
The Explosive Object Mortar Contraption fires explosive shells over great distances. The only drawback to the great range is that it takes a while for the projectile to reach its target. Unlike other towers, the Mortar has a minimum range of approximately two blocks regardless of its upgrade level. The actual damage per shot is vastly increased if hitting multiple enemies within the splash radius of the mortar shells.
Strategies:
Mortars are very effective on closely packed ground units. However, without proper crowd control by the player they are pretty useless. Since a mortar grenade takes a long time to land it may very well miss its target if it runs too fast. Also, as it will fire on its nearest target it is imperative that no mobs are allowed to break out as forerunners, thus drawing fire from the mortars away from the bulk mob-cluster. Therefore it is pointless to only have mortars without proper placement of Slow Fields and careful use of the Freeze Gun.

Amp Field[sanctum-series.fandom.com]
Rank: D
Info:
The Amp Field increases the damage inflicted upon ground enemies within its boundary.
Strategies:
Use in places where it will be easy to Freeze enemies in place and fill them with bullets, or where your Towers can make use of the Field.
An apt summery from EolSunder of why I favor the Slowfields over the other two types:
https://steamproxy.net/app/91600/discussions/0/1520386297702502156/

Kairos[sanctum-series.fandom.com]
Rank: E
Info:
The Kairos is a tower that slows down airborne enemies. Every few seconds, it creates a temporary spherical field that slows down air targets that pass through it. The Kairos was introduced in the Old City update.
The Kairos slows down enemies by 55%, each sphere lasts for 5 seconds, and the Kairos' range is 10.4 tower lengths.
Strategies:
I have never used it, but slowing down Air Lumes would be nice if it wasn't so expensive. This doesn't seem cost effective on Insane.

Penetrator[sanctum-series.fandom.com]
Rank: D
Info:
The Penetrator fires beams of plasma that pierce through enemies and can hit up to 10 enemies in a line. It is incapable of pitching up or down, so it can not hit a Runner when it is on a flat, level surface.
Strategies:
Use the Penetrator in long, straight lines, preferably with the enemies moving away, to maximize its damage. Because of its low height, combining it with a Holo tower is very effective. Since it shoots beyond its vision's range, it does not matter as much how far away the Penetrator is placed.
It can shoot through anything, even blocks.
This seems like it would be most useful against enemies with shields, such as the Tank or Hoverer. I have used it a few times, but its slow DPS is why I favor other towers.

Killing Floor[sanctum-series.fandom.com]
Rank: E
Info:
The Killing Floor is a field that damages enemies that tread over it. It is capable of hitting multiple enemies. It has a cooldown period after making an attack.
Strategies:
Unlike most towers, Killing Floors reliably hit the weak spot of Hoverers.
Killing Floors can be used to sort Hoverers out before they draw the fire of other towers to themselves which cannot harm them and is better used on other enemies.
Killing Floors work very well against runners, especially if you use a few killing floors after another. Walkers and Big Walkers are also effectivly damaged.
Killing Floors are useless against soakers
An apt summery from EolSunder of why I favor the Slowfields over the other two types:
https://steamproxy.net/app/91600/discussions/0/1520386297702502156/

Drone[sanctum-series.fandom.com]
Rank: E
Info:
The Drone tower releases a swarm of drones that damage an enemy heavily over a long period of time and ignore armor. An enemy can only be attacked by one swarm at a time. Each Drone Swarm fires 100 shots with a 0.15 second interval.
Strategies:
The Drone tower is best built at the entrance of your maze (or at any point where they have to return after a good while). This is because it takes a long while for the drone tower to deal its full damage, so the more time it has the more useful it is.
According to the Wiki, this has one of the lowest DPS per Resource spent in the game. Honestly, I will never use it.

This section will take a bit to complete, as I have gotten all of these, and need to remember how I got most of them.
Edit : 10/02/23 I used a achievement manager to lock the secret ones, so I have to get them again, shhhhhh! :D Also, I've been playing this game for over 10 years O_o holy crap lol

I got some help from the already complete guide : https://steamproxy.net/sharedfiles/filedetails/?id=152221535

Feel free to use that guide instead, no worries. Some of the videos in that guide are dead though, so I will post my own as well.

No secret or story achievements on Complex, Aftershock, Cavern, Slums, Christmas, Corporation, or Whirlpool


Voyage au centre de la Terre
Secret Achievement
Map: Mine


In the North east corner of the map, go underneath the up ramp and jump/fall down onto the lower platform with flashing lights. Follow the path and go through the teleporter. Enjoy the fun dialog. The achievement will pop when you take the teleporter back to the surface.


Seven Sisters
Find the Babushka Doll on Mine
Map: Mine


Walk to the main bridge and head down the south/left side about halfway. Hop up on the barricade, and then down to a ledge sticking out a bit. The doll is on a box there.


The Plot Thickens
Secret Achievement
Map : Bridge


Head to the Core. On the bridge leading to the core, hop off and land on the platform underneath it. I nearly missed lol. Turn around and head into the room, it should pop.


Lunch box
Find the sandwiches on Bridge
Map : Bridge


From the start, head past the Core to the bottom right/ south east part of the map. Pass the guy typing to the second long walkway on the right/to the south that ends in a door. Keep going until you reach the end of the platform/reach the door and turn left. Walk along the ledge until you reach the end, the sandwiches are beneath you.


The Monument
Secret Achievement
Map : Arc


From the teleporter, underneath the south-most planter box, there are two pipe ledges that stick out. Jump down there, then hop over the barricade onto the platform. A little further down, hop back over the barricade onto another pipe platform. Follow this path, hopping across the gaps until you reach the end, underneath the south Lume spawn point. I fell once lol. You will hit a invisible collision box at the end and fall down onto some old panels. Follow the panels until you reach the monument in the clearing.


Meet the President
Meet the President on Arc
Map : Arc


From the teleporter, underneath the south-most planter box, there are two pipe ledges that stick out. Jump down there, then hop over the barricade onto the platform. Follow the platform path past the terminal and the Babushka doll box and into the Teleporter around the corner.


Keep quiet
Secret Achievement
Map : Glade


This achievement requires you to reach wave 14 on Glade. Once you do, head to the left side of the map, and go underneath the maze. A panel will open revealing a teleporter. After going through, follow the path until you reach the glowing monument room. Head left and jump up the broken ramps, then follow the path to the glowing Core suspended behind a field. Once you walk through the field, you will teleport back outside and the achievement will pop.


I Love Strawberries
Guide Box Boy to the Giant Strawberry
Map : Glade


I recommend having a 4-shot Sniper for this achievement. From the starting point, head to the right/east side of the map. You will need to place a block/teleporter to be able to reach Box Boy. He is sitting on top of a crate at the bottom edge of the right/east maze. You can use either the Sniper or the Gatling gun to shoot Box Boy to the strawberry. The strawberry is south-east of Box Boy, to the left of a boulder, hidden in the bushes. Careful to not lose him in the bushes.





Beach Party!
Get the party started on Glade
Map : Glade


You can do this achievement at any time on the Glade map. From the starting point head to the left/west side of the map. Go past the end of the maze area and then turn south. You will see the party all set up. Start the wave, then shoot the lid off the grill, shoot open the parasol, and shoot the radio to turn it on. Enjoy the party!


Sweet
Secret Achievement
Map : Facility


You will need to reach wave 20 on Facility in survival mode on any difficulty. To the south of the Core, there is a platform with a circular staircase. Head up and then head down the hallway. The door should open after you hit wave 20.


Domo Arigato, Mr. Roboto
Find the Robot buddy on Aftermath
Map : Aftermath


You can use either the REX or Grenade launcher for this. In the lower right corner of the map, you will need to build a block and a televator next to it. Hop on the light fixture? and shoot down at your feet while jumping. You might need to jump first, then shoot to create more lift.


A Future Friend
Secret Achievement
Map : Yogscave/Below


In Yogscave/Below, head toward the left side of the map and off the overview. Your friend is behind the tank.


Strawberry Fields Forever
Secret Achievement
Map : Invasion

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Text version


Chilla Grillen!
Secret Achievement
Map : Chasm


In Chasm, towards the bottom left of the map, there is a vine/root? that you can jump towards and walk up. In that area, there is a grill with an icicle hanging above it. Shoot the lid off the grill and then shoot the icicle to make it fall.

Notes:
Unless the achievement specifies, you can play on any Difficulty and Game Mode.

Spray and Pray
Reach wave 10 only having built Blocks and Gatlings.

Like it says, you can only build Blocks and Gatlings. Nothing else and no upgrading weapons.
Best map to play this on is Mine, or any map that does not have air enemies, on Easy difficulty.

Scatter Brain

OVER 9000!

Legion

Without Number

Hope Rides Alone

Copyright Troll

Below are images of the Mazes I used for each of my Insane runs.

If you need the specific walkthough, see my other guide :

https://steamproxy.net/sharedfiles/filedetails/?id=2711925704

Mine



Bridge



Arc



Glade



Complex



Facility



Aftermath



Aftershock



Cavern



Slums



Yogscave/Below

Waves:


Israphel:


Christmas



Corporation



Invasion



Chasm



Whirlpool