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.
This attack is widely considered as his hardest attack.
Shoots 8-way blood shots.
Jumps into the air and tries to land on Isaac, leaving a small puddle of Red Creep and shooting 8-way blood shots.
Spawning a large puddle of Creep.
Both of his eyes are detached from their sockets from the beginning. They travel diagonally around the room.
Since The Bloat will attack you with his blood-beams if you are standing to the front or sides of him, it is best to attack him from behind.
If you're not behind him or he backs himself to the back wall, try to shoot tears diagonally at him while moving without entering his "blood-beam-area".
Because the AI of his eyes are derived from Boom Flies, obtaining Skatole can slow down his eyes and make this fight slightly easier.
There is a way to lock him in a pattern of constantly firing his blood-beams, similarly to Monstro II, but this takes incredible reaction, since the attack comes so quickly, unlike Monstro II. Simply stay in front of him until he fires his blood beam, then attack him from the side. When he fires his side blood-beams, move back in front of him. Lather, rinse, and repeat.
Upon the start of the battle, it is worth knowing that when entering the boss room directly beside or in front of The Bloat, it will immediately attack you with its Blood Beam. Unless players are prepared for this, it will almost always lead to unavoidable damage.
Bloat's eyes seem to derive from Boom Flies in their AI as they move in a diagonal pattern and are slowed by Skatole. If you are killed by an eye, similar to Peep, the picture on the death note is of a Boom Fly.
When you get killed by the Bloat, his picture on the death note is that of Peep's.
Killing Peep in The Caves increases the chance of meeting The Bloat in the Womb.