This guide is accurate as of version 0.85b of the game.
This guide is accurate as of version 0.86b of the game.
This guide is accurate as of version 0.91b of the game.
This guide is accurate as of version 0.95b of the game.
This guide is accurate as of version 0.952b of the game.
This guide is accurate as of version 0.958 of the game.
Updated for version 1.01.00 (also, the owlhawk section has been improved)

The bosses for levels 9 and 10 do not have definite weaknesses.

Each of the first eight bosses has exactly one weakness, and each weapon has exactly one boss who is weak to it. Each weapon is organized in the table that follows in a loop. Each weapon in a loop is effective on the boss that gives the next weapon in the loop. When the end of the loop is reached, the first boss is weak to the last weapon.

Charging an attack usually doubles the damage. All of Nina's main weapons can be charged, and when charged the attacks pierce on kill. Most of Ace's main weapons can be charged. With the Core Aug Dracopent's Claw, an Ultracharge can be performed, which usually triples the damage.

For Ace, attacking with most weapons on the ground will perform a combination attack, with varying damage and range on each hit. When multiple damage values appear in the table below, they indicate the damage of each hit in a combo. Combos are either 2 or 3 hits long, depending on the weapon.

For Ace, damage against bosses from all hits in a combo aside from the first is reduced slightly.
(This does not affect Plasma Blender.)

For Nina, using either Star Beam or Forkalator and hitting any target with multiple shots from the same press of the button, will reduce the damage of the excess shots to 25% of their normal value.
For instance, if you were to use Forkalator and all 3 shots hit the same target, one of them will do 8 damage, and the other two will do 2 damage each, for a total of 12 damage.

Each power has a special effect when used against the boss who is weak to it.

Additionally, each power has a unique special ability when used in stages.
The following chart shows information on the special abilities of each weapon.

{updated on 11/18/2017}

Collecting the entire set of Owlhawk Armor will result in "juiced" powers.
This affects each of the eight powers differently.

Here is a link to a thread that discusses the Owlhawk the Wise set bonus.



Effects:
Quintlaser: Initial charge level +2, can be charged to +3 and +4
Splinterfrost: Icicle breaks into a full circle on impact (up to 24 individual shards)
Forcenova: Creates an additional nova at the enemy's location whenever any nova kills an enemy
Flameshield: Made of 8 flames instead of 4
Vera: Twice the rate of fire
Boomerang: Two extra boomerangs for each use of the weapon
Shadespur: Two extra shadespurs at right angles with the same speed as the original
Mortar: Bursts into a cluster of 5 smaller mortars when it hits something

Screenshots:

Level 9 Boss: Doctor Brighton Sharp

Doctor Sharp has 7 different abilities, but will start the battle with only 4 of them.

Every time you take off a quarter of his maximum hitpoints, he will learn a new attack.
The order in which he learns new attacks is random, but he will have all of them by the end of the battle.

All of Doctor Sharp's abilities are based on the abilities of the bosses you have already defeated.
(except perforator's)

Doctor Sharp has these actions available from the start:
Attacks using Splinterfrost
Attacks using Mortar
Attacks using Shadespur
Summons a shield projecting Maintcore

Doctor Sharp learns these actions:
Summons several walls of Quint Lasers from one side of the room
Summons a wheel which bounces around the room
Summons an orb of fire and a leash

Both the wheel and the orb will only be summoned once each, but cannot be destroyed.
If you touch the leash connecting the orb of fire to Sharp, it will injure you.

Countering his abilities with your own:
1. Mortar can be used when Sharp summons the shield scarab. You can use it on either of them.
2. Flameshield can block all his splinterfrost attacks.
3. Flameshield can also stun his boomering blade wheel.
4. Vera does the same thing to Sharp's lasers that it does to Kur's.
5. Splinterfrost will freeze Sharp's Orb, preventing it from moving and disabling the line it forms.

Level 10 Boss: Doctor Arlan Flat

This is it, the final boss!

During this battle, in addition to the boss, you will also be attacked by copies of Nina and Ace, and must deal with environmental hazards and tricky platforming.

To damage this boss, you are meant to attack him from behind his shield.
But first you must get past the spider. To cross under the spider, attack its legs.

Each time you deal enough damage to Arlan or enough time passes, he will move to the other
side of the room and you will have to make it through new hazards and new platforming. These are randomized every time he does this.

Regarding hazards, any laser generators that you disable will stay offline even when the room changes, and can be disabled in advance if you use a Force Nova where they may appear later.
However, fire turrets and disappearing blocks will be reset when the room changes and so can only be frozen temporarily.

Tip: If you have armor pieces that grant life or energy on kill, you can regain those resources
when you destroy the copies of Nina and Ace that show up during the battle. New ones will always
show up in the middle part of the room after each cycle. This means you can regain an infinite amount during this battle.