Key Bum

Key Bum is an unlockable passive item added in The Binding of Isaac: Afterbirth.

Effects

Spawns a familiar that follows Isaac around and collects Keys, dropping random Chests in return.
- Spawns almost exclusively Chests, Red Chests, and Locked Chests, with a very slim chance to spawn another type of chest or a Grab Bag.
This item belongs to the Super Bum set. Collecting three items from this set will transform Isaac's bums into Super Bum.

Key Bum will not pick up Golden Keys.
Key Bum will pick up Charged Key without additional benefit.
- Key Bum will leave a Lil' Battery behind when picking up Charged Key.
From a scoring perspective, Keys that Key Bum picks up count towards your Schwag bonus on daily runs.
Key Bum does not join the line of familiars that follow behind Isaac.

BFFS!: Familiar is bigger and drops chests more often.
Flat Penny: Chests frequently contain pennies, which have a chance of spawning more keys for Key Bum to pick up, possibly lead to a loop.
Gilded Key / The Left Hand: Works as expected.
Guppy's Eye: Allows Isaac to choose which Locked Chests are worth opening and which to pass, thus saving keys. Great for min-maxing.

Bug!	If Credit Card is used in a Shop with Keys, Key Bum will not be able to pick up the free keys. This can be fixed if Isaac leaves and re-enters the shop.