Isaac turns into his cat Guppy after picking up any three distinct items in the following list. In this form, Isaac gains Flight and will spawn one blue fly every time an enemy is hit with a tear. Flies do not spawn when dealing damage without tears (except Brimstone), such as with Mom's Knife or Epic Fetus.
||Sets the amount of red heart containers to 1, but gives Isaac 9 extra lives. After dying, Isaac is teleported to the last safe room. New heart containers can be obtained after picking up this item, but after each death, the number of heart containers is set to 1 again.
||Grants Isaac a permanent 50% chance to respawn with 1/2 of a red heart after death.
||Increases chance of finding gold chests and normal chests, but reduces chance of finding pickups.
|Guppy's Hair Ball
||Loosely follows behind Isaac. Can be swung like a flail by rapidly spinning Isaac in a circle. Grows bigger by killing enemies.
PC XWN6 1YWH (Basement I - Curse Room above spawn contains 2 Red Chests and Stone Chest, Guppy's Collar, Guppy's Head and Dead Cat respectively)
PC 7TC3 43F1 (Cellar I - Curse Room above spawn contains 2 Red Chests and Stone Chest, Guppy's Collar, Guppy's Paw and Guppy's Head respectively
PC W82M ZL3F (Basement, Eden only - Start with Guppy's Head, golden treasure room contains Guppy's Paw, silver treasure room contains Guppy's Tail)
3DS F4GJ 7ZHK (Caves II, Boss Challenge Room, three red chests with Guppy's Tail, Guppy's Head and Guppy's Paw)