| Floors of
| Base Health||600|
|Items Dropped||Boss Pool|
Mega Fatty is an enemy in The Binding of Isaac: Rebirth that is present as Both a boss on The Caves floor and as a Monster on later floors. It is a giant version of a Fatty.
Mega Fatty will start in the middle of the Boss Room, possibly spawning alongside two Dips. During the battle, Mega Fatty will perform one of many attacks. The attacks Mega Fatty can perform are as follows:
- Mega Fatty will jump in the air, leaving the player's vision. Mega Fatty will later land on the floor at the position in which Isaac was located when Mega Fatty initiated the jump, leaving a large puddle of Creep beneath him upon landing. The player should quickly move out of the way, as, unlike most bosses, Mega Fatty will move and land very quickly whilst in the air.
- Mega Fatty will release flatulence, consequently releasing a barrage of fecal tears at Isaac.
- Mega Fatty will inhale, sucking in all entities in the room towards him (this includes bombs). Afterwards, Mega Fatty will vomit, shooting a barrage of homing mortar tears at Isaac. Although the homing effect is very low, the player is advised to keep moving.
- Mega Fatty will release flatulence, spawning two Dips and possibly damaging Isaac if he is too close to Mega Fatty.
The player is advised to keep away from Mega Fatty as to avoid his jumping, sucking, and flatulence-oriented attacks. Whenever Mega Fatty attacks, it is recommended that the player move away from the position that they were in when Mega Fatty initiated the attack. The player should look at the shadows of his vomit projectiles in order to calculate their position.