|Location:||Black Powder Mine|
|Guns in the Deep|
|The leader of the Skusket, this massive skull is wreathed in dark clouds of gunpowder and hatred.
It will not permit anyone to pass.
- Rolls around the room, firing a large circle of bullets when it collides with a wall.
- Darkens the room, teleporting around randomly and firing lines of five bullets that bounce once before eventually dissipating.
- Shoots a spiraling stream of bullets from both eyes, which will move independently and overlap.
- Rapidly fires bullets randomly towards the player.
- Hops in a circle, firing rings of bullets outwards.
- When Cannonbalrog rolls around the room, try to dodge roll through the waves it sends out and avoid letting it roll into you unless you are playing as The Bullet or have an item that negates contact damage.
- When it does its teleporting attack, try to stand where the bullet lines meet so that you can roll through both of them. Try to either stay near the middle of the arena or near a corner during this attack to avoid being caught off-guard by bouncing bullets.
- Try to roll sideways through the spirals of bullets, as this leaves you more time to dodge roll again if another bullet approaches. Alternatively, stay farther from Cannonbalrog and weave in between the bullets.
- When it rapidly fires bullets randomly, try to keep your distance and dodge.
- When he hops in a circle, either keep your distance and weave in between the bullets or simply roll through the rings.
- If you are playing as The Bullet or have an item that negates contact damage, you can stick yourself between Cannonbalrog and the wall to get it stuck in place during its rolling attack and be unable to attack.
- Cannonbalrog can be damaged by Bomb or Dark Marker while using its teleporting attack. The homing bullets from The Scrambler can still track Cannonbalrog during the teleporting, but damage comes afterwards.
- Cannonbalrog can also be damaged by swinging Blasphemy at its location of disappearance during its teleporting attack.
- Cannonbalrog can also be damaged by the flash-explosion caused by BSG's shots during the teleport attack.
- If Cannonbalrog is frozen, it will leave behind a path of ice when it performs its roll attack.
- Guon Stones do not block Cannonbalrog's larger bullets.
- It is possible for Cannonbalrog to become stuck on companions while rolling around in the room, given the companion can deal contact damage.
- This boss's name is a reference to the Balrog from "Lord of the Rings".
- The reference is further cemented by the fact that the Cannonbalrog is fought in the Black Powder Mines, and the original Balrog is encountered in the abandoned Mines of Moria.
- The Ammonomicon Entry is a reference to the scene in the book and the movie, where Gandalf tells the Balrog, "You shall not pass!"
- The name of the entry - Guns in the Deep - is a further reference, as a dwarven book that the Fellowship discovers mentions the sound of 'drums in the deep' as a precursor to the attack of the Balrog and its allies.