The Bloat

The Bloat is the posthumous version of Peep found in Necropolis and all environments of Chapter 4.

Behavior

The Bloat's eyes bounce around the room immediately at the start of the fight.
Fires eight blood shots in all directions.
Jumps into the air and tries to land on Isaac, leaving a small puddle of Red Creep and firing eight blood shots in all directions.
Creates large puddles of Red Creep.
Fires 2 Brimstone lasers in front of him or to both sides of him, depending on the location of the player. This attack is not telegraphed.

Green: Fires three Greenish Red Ipecac projectiles instead of blood shots, and spawns 1-2 Chargers whenever he creates the large puddles of Red Creep.

The Bloat in-game.
The Green Champion Bloat.
The Bloat as one of Delirium's forms.
Sketches for The Bloat and other bosses for the original Binding of Isaac's Wrath of the Lamb DLC.

The usual tactic is to stay behind The Bloat and dodge any projectiles he may shoot behind him. If he backs himself to the back wall, try to shoot him diagonally or wait for him to use another move before attempting to strike him sideways or from behind. Bombs are highly recommended to be used here if you are a new player.
If you stay at his right or left, but not high enough, his brimstone-like attack will be fired, but it won't hit you. It is recommended to do so to get a few free hits.
If you start the fight directly below him or to his left or right, move out of the way immediately to avoid getting hit by an immediate Brimstone blast.

The Bloat's eyes can be destroyed with Chaos Card, Euthanasia, God's Flesh or Little Horn, making the boss fight easier.

The Bloat was added in the Wrath of the Lamb DLC for the original The Binding of Isaac.
Bloat is a medical condition in which the stomach becomes overstretched by excessive gas content.
Corpses also bloat during decomposition due to the excessive build-up of gas-releasing bacteria. Due to being an undead version of Peep, this phenomenon could be what the Bloat’s name is referencing.
The Bloat's eyeballs look slightly different than Peep's.
The Aprils Fool challenge replaces all bosses with The Bloat as a reference to the exceptional hatred some fans express towards this boss.

Bug!	The Bloat's Eyes have the same collision radius as The Bloat itself, which results in the eyes being difficult to dodge since the hitbox doesn't match up with the eyes' visual size.