Bosses are strong enemies found at the end of every floor in The Gungeon. Defeating a boss allows the player to advance to the next main floor.
Upon being killed, bosses drop a weapon or item of random quality, several Hegemony Credits, and one to three pickups such as hearts, ammo, or keys. Bosses will always drop a gun if the player has not yet picked up a gun on the current floor. If a boss from one of the five main floors is defeated without getting hit, they will drop a Master Round as well. Clearing a boss without getting hit will also cause it to drop doubled Hegemony Credits.
- When the player enters the past, they will lose their items and guns, but will keep blanks and armor.
- Every boss has a DPS (damage per second) cap as a way of stopping players from dealing high amounts of damage over a short time, so guns with high fire rate or high damage can't destroy bosses in seconds.
- The DPS cap of bosses varies per floor:
- The DPS cap is applied across a 3-second window.
- The most damage a single shot can deal is equal to triple the floor's DPS cap.
- In Boss Rush, bosses have no damage per second cap.
- In co-op, the DPS cap is increased by 70%.
- The DPS cap is ignored by Glass Cannon, Makeshift Cannon, Yari Launcher, Boxing Glove's 3 star charged super punch, and High Kaliber's souls.
- The DPS cap is ignored if a weapon deals 1000 or more damage with a single projectile.