Boil

Boils are stationary enemies with the ability to regenerate. Revelations added the following variants.

Bomb Sack
Bomb Sacks are uncommon enemies exclusively found in Burning Basement and can be spawned by champion Raging Long Legs. They were added in the Sin Update.

Like regular Boils, they can regenerate when damaged. In some rooms, they can spawn spiders when at full swelling, though they will stop this attack if no other enemies are alive in the room besides Spiders and Bomb Sacks. Their main ability, however, is that whenever touched by flaming enemies (Flaming Gapers, Flaming Hoppers, Flaming Fatties, Crispies or Raging Long Legs' fires), their fuses ignite and they begin to shrink. When killed in this state or if allowed to finish shrinking, Bomb Sacks explode, damaging obstacles and players around them but dealing minor damage to enemies. This is sometimes used to uncover rewards barred off by rocks without the need for player Bombs.

Bomb Sacks do not need to be killed to clear the room, similar to Necragmancers.

Trivia

 * Bomb Sacks are one of the few enemies added in Revelations that appear in the main path. The others being: Drifty, Pucker, Brother Bloody, Smolycephalus, Mother Pucker, Aerotoma and Chicken.