You probably already know what I'm talking about if you're reading this, but for all three people who've never fought against one before (god bless), a Battle Engineer is an Engineer who's playstyle focuses on more aggressive play. While some Battle Engies use other melees, for the most part they use the Gunslinger. A weapon that gives the Engineer 150 health and the ability to use mini sentries. Mini sentries only cost 100 metal to build (opposed to the normal sentry's 130 metal) and build twice as fast at the cost of not being able to upgrade them. It also gives you a guaranteed crit for every third successful consecutive melee hit you land, however most players don't use this. Now, we all know sentries are annoying to deal with. Having to fight an object with rapid fire and perfect aim is something everybody inherently finds annoying. Now imagine the person who built that sentry not having to think about where they put said object because they can replace it within a few seconds with little penalty. Now with that out of the way, let's go over a few general strategies.

A lot of how you approach a Battle Engie heavily depends on what weapons they're using. So if you know an Engineer is using a certain weapon, here are a few ways that can help you deal with them.

Frontier Justice - Try to make sure you take out the Engineer before you destroy his sentry. You may get beat up a bit, but sometimes a revenge crit can be the difference between life and death. Along with this, look at the kill feed. If the Engineer's name keeps popping up or they have a killstreak going, be cautious.

Widowmaker - Odds are that this person is running the stock Pistol to cover their weakness from far range, meaning they aren't using one of the two secondaries that would make it difficult to destroy their sentry. You should be fine destroying it and you don't have to worry about revenge crits, but be careful when you get up close. Picking another class that can deal with them at long range can make it so they can't land a good meatshot on you.

Pomson/Rescue Ranger - I'm putting these in the same category since both of these players are similar. In short, they're clueless. Once that sentry is down, they're ♥♥♥♥♥♥.

Wrangler - This guy's gonna be really annoying to deal with. Like with the Frontier Justice, take the Engie out first and the sentry later. The wrangler may have aim assist, but the sentry no longer has perfect aim which gives you a slight advantage. Make sure to get close to the Engie since it's harder to aim it at closer range.

Short Circuit - It's best to just switch to a hitscan class if the Engie has the Short Circuit. You're probably not gonna have fun trying to destroy a sentry while the Engie just keeps deleting your projectiles.

Southern Hospitality - This guys probably sick of dealing with Spies. Normally the fire damage downside wouldn't really matter on Engineer since he's not around Pyros much, however they'll be on the front lines more and thus be more vulnerable to getting attacked. This is the only situation I'd specifically recommend going Pyro to combat a Battle Engie, however don't count on this since most Battle Engies don't use the Southern Hospitality.

Jag - This guy is probably gonna try to set up a Level 2 or 3 sentry by the enemy team. These guys tend to be a bit more risky with their playstyle, however their inability to heal buildings quickly means they can be easily overwhelmed. Try teaming up with somebody if you see a Level 3 sentry.

Eureka Effect - These guys aren't really concerned about their sentry. They like to play another similar sub-class called Ninjaneer. These guy will put hidden teleporters around the map to sneak behind enemy lines and taunt to escape back to resupply when ♥♥♥♥ gets messy. Check all the props on the map for teleporters (roofs, bushes, etc.), because odds are there's a teleporter hidden somewhere. When you find the teleporter, DO NOT stand on it while destroying it or you might get telefragged.

Now that we're done with the general strategies, it's time to get into some class specific ones. Before we get into class specifics however, all of these strategies are under the assumption that the Engineer in question is using the Gunslinger. That being said, let's get into it.

Make no mistake, Scout is the absolute worst class to use to fight a Battle Engie. However, there are ways that can help you deal with them. First thing's first, equip a Pistol. Anyone will do, they all have their own upsides for dealing with sentries (clip size, firing speed, damage output). Try taking their sentry out from a distance. Now at this point, one of three things will happen.
1. The Engineer isn't by their sentry and it goes down. Go after the Engineer who built it (assuming they're still alive) now that their defenses are lowered.
2. The Engineer will try to close the distance and take you out. Use this opportunity to land a few good meatshots on them. Once that's done, finish off the sentry with your pistol.
3. The Engineer notices and they pull out the Wrangler. At this point, it's pretty much game over for you, just switch classes. Unless you pull a good flank on the Engie, you're as good as dead.
As for your primary and melee? I'd just stick to the stock Scattergun, but if you have good aim, then I recommend the Force-a-Nature or Soda Popper since they can get the 150 damage needed to kill them off faster. For melee I'd suggest the Candy Cane since you get a small health pack on kill, helping you recover a bit of damage the Engineer/ Sentry may have caused.

Soldier is a great choice to go up against a Battle Engie because of how versatile he is. Now your choice of primary should be obvious, the Direct hit. The Direct hit can easily one shot the little bastards. For your secondary, I recommend a shotgun of sorts. Either stock or the Panic Attack. Reserve shooter isn't optimal for this situation since you can easily airshot them if you pop them up in the air with another shotgun or another rocket and kill them regardless. For melee I either recommend the Escape Plan or Disciplinary Action. The Escape Plan can help with a get-away if you just killed them or they're about to kill you. As for the whip, it's good if you miss all your rockets/shells because of the extra melee range and not being held back by the switch speed or honor bound of the Half Zatoichi. And with random crits, this thing will kill them in one hit or leave them fighting for their life.

Like Scout, I generally wouldn't recommend picking Pyro to fight against a Battle Engie. There are ways to do it, but for the most part I'd recommend switching classes. But you're stubborn, I get it (I am to) so I'll go over a few ways that could help. If you can find a way to close the distance without getting gunned down, then I'd say use a shotgun. If you can't however, then flare guns all the way. Now I'd usually recommend the Degreaser for your primary, but switch speed won't exactly come into play much here. In this case I'd recommend stock and take the "If I'm going down then you're going down with me" approach. For your melee, I'd say the Back Scratcher. The Powerjack is good, but the damage vulnerability can really screw you over if you get caught off guard by a mini sentry, plus the health bonus from health packs can really help for when the battle is over.

Demo is one of the best options to fight an Engineer. Demo was essentially designed to counter Engie. After all, there's a reason he's called the DEMOLITION Man. Stock Demo will do just fine, but there are a few utilities that could help you out. The Loch-N-Load is a good Engineer counter, but isn't really necessary since mini sentries get oneshot by a direct hit from any Grenade Launcher anyways (aside from the Loose Cannon), so in this case I'd recommend the Iron Bomber due to the slightly larger hitbox of the pipes. Now while the Loch-n-Load is good for covering more range, there's another weapon that could help cover that. The Quickiebomb Launcher's faster charge time can easily land stickies across the map within seconds. Even against a wrangled mini sentry, you could sticky snipe it with four stickies. For melee, stock is fine, maybe the Ullapool caber if you want to take the flashy "go down with me" approach that I mentioned earlier. That being said, there are two very important pieces of advice for fighting Battle Engie as Demo.
1. If they have the Short Circuit, try to juke their three energy balls, then take them out. If you can't, then switch classes.
2. NEVER go full Demoknight against a Battle Engie. You can try hybrid knight if you want, but never approach them without a Grenade Launcher.

Heavy is also a pretty good candidate to fight a Battle Engie, hell I'd argue he's the best choice against a Battle Engie.. Heavy's attributes can easily deal with mini sentries. He can easily tank a wrangled mini sentry and Heavy doesn't need to worry about the Short Circuit since he's a hitscan class. I'd recommend the Timislav since you could snipe the sentry while you're out of it's effective range. As for your other weapons, Id recommend the Sandvich (or the Second Banana if you prefer it) and the Fists of Steel just in case you need to get to an area past the sentry or make an escape. All in all, pick Heavy if you really want to give that Battle Engie a bad time.

While you can go Engie to counter Engie, it wouldn't exactly be my first choice to do so. If you really want to stick it to that Battle Engie, play more defensively. As they say, the best offense is a good defense. Good luck taking down a Level 3 with a mini sentry and a shotgun. If you're feeling a bit braver however, you can still go Battle Engie as well. I don't really have much to say for Engineer to be honest, just try defending.

Now Medic really shouldn't be fighting anyone in general, but you can certainly help your teammates take out the Engie. Now for the most part any Medi Gun will do, but in terms of most to least useful, I'd say Vaccinator>Quick Fix>Stock>Kritzkrieg. The Vaccinator can be good when dealing with sentries with it's bullet resistance and making an escape can be easy with popping one of your four ubers, the Quick Fix can help you make an escape if you have an explosive jumping teammate with you, stock is alright is an okay choice in general but you're kinda screwed if you're left alone, and the Kritzkrieg is in a similar situation with stock but you can't really get a good escape if you have an uber, Primary and melee are simple, Crossbow and Ubersaw. Take out the sentry from a distance with the crossbow and hope for a melee crit if anyone gets too close. You have some defense options, but for the most part you're at the mercy of your teammates.

While not a typical choice to counter Battle Engie, Sniper can absolutely destroy a them. A simple fully charged shot could easily take out an Engie or his sentry. Normally I would recommend the Jarate/Bushwacka combo, but you most likely be getting close to the Engineer, so for this I'd recommend full stock, maybe the Cozy Camper if they're pestering you from a distance. If you can stomp people as Sniper, you can stomp them as well.

Spy is easily a great choice to counter Engie. Now since it's pretty much a guarantee that the Engineer will be using their sentry, equip the Diamondback and be prepared to pop a crit out of your ass if you fail the stab. Now I wouldn't normally recommend this weapon, but if you're only focusing on the Battle Engie, equip the Red Tape Recorder. It takes longer sap their sentry, but that means they can't destroy it themselves and get their revenge crits (assuming they have the Frontier Justice) or slam down another one. This forces them to do one of two things.
1. Un-sap the sentry and hope they don't die while they do.
2. Forget about the sentry and hope they land a good meatshot.
As for your Knife and watch, equip anything you want (I use stock for both) since there really isn't a bad option for either.

While a Battle Engie can destroy you in combat, there are many ways you can destroy them. Just remember the tips I shared with you today and soon enough you'll be recreating the Battle of the Alamo. Now get out there and destroy those Texans.