He has a total of five items related to him in the game, of which collecting three (excluding Guppy's Hair Ball) will transform Isaac into Guppy.
Transforming into GuppyEdit
Dead cat, Guppy's tail, Guppy's paw or Guppy's Head have a unique feature: Isaac can permanently transform himself into Guppy when collects three of them. They can potentially be found in the Devil rooms. Excluding Dead Cat, all of the Guppy items are exclusive to Wrath of the Lamb.
Transforming into Guppy unlocks Guppy's Hair ball.
- The Parasite does not completely eliminate the ability to spawn Attack Flies when Isaac's tears strike an enemy.
- Chocolate Milk charged Attack Flies still instant kill Black Fly, Attack Fly, Pooter and Fat Fly.
- Tear-firing Familiars such as Brother Bobby, Demon Baby, Gish, and Little Steve. Any tears fired by Familiars which strike an enemy will spawn Attack Flies.
Found in the Devil Room, Curse Room, Red Chests, and as a drop from Super Pride. Isaac's heart containers are set to 1 and he is given 9 lives, as well as a dead cat head Familiar. Health upgrades can be taken as normal, but upon dying, his heart containers will be reset to 1 again.
Found in the Devil Room, Curse Room or Red Chests. Once collected, Chests have a 1/3 chance of replacing any other non-specific Pick Up.
Found in the Devil Room, Curse Room or Red Chests. Spawns 2-4 Attack Flies upon activation to damage enemies. Recharges after clearing one room.
Loosely follows behind Isaac. Can be swung like a flail by Isaac rapidly spinning in a circle.
Deals damage when it collides with enemies. If an enemy is killed by the ball, it increases in size up to a maximum limit. The larger the ball becomes the easier it is to swing, the larger its collision circle becomes and the higher its damage becomes. Size is reduced at the start of each floor. Collecting Guppy's Hairball does not count towards becoming Guppy.
- If the third Guppy item Isaac picks up is an activated item, the game may bug, so he may have to switch out the final active item before becoming Guppy.
- It can be assumed that Guppy is dead by the time Isaac explores the world under the trapdoor, since pieces of him can be found throughout the adventure. Eventually Isaac can also find Dead Cat which represents Guppy himself.
- Guppy is actually a reference to Edmund McMillen's own pet cat called Guppy.
- Guppy appears in the Castle In The Darkness Prologue, where his curse brings you to an alternate level.
"Guppy's Hairball" - Collect three Guppy-related items in a single playthrough.