- Grants a familiar that follows Isaac and always appears first in the familiar chain.
- While firing tears, King Baby stops moving and glows white.
- While King Baby is stationary, other familiars remain stationary as well.
- Shooting familiars will fire tears in the direction the player is firing.
- Shooting familiars fire at nearby enemies automatically.
- Familiars that have charged attacks will operate on similar rules to Marked: they will immediately fire at full charge, and variable-charged attacks will be released earlier the closer that King Baby is to the target.
- When Isaac stops firing tears, King Baby moves rapidly back towards Isaac.
- This item belongs to the Conjoined set. Collecting three items from this set will transform Isaac into a three-faced version of himself.
- King Baby will move back towards Isaac during Isaac's hurt animation, even if a fire button is still being held.
- Abel will still reflect Isaac's movements, and not King Baby ones.
- Lil Delirium depends on which familiar form it takes.
- Duplicate King Babies, such as those granted from Box of Friends, will cause your familiars to follow the last King Baby added.
- Familiars unaffected by King Baby include:
- ???'s Only Friend
- ???'s Soul
- 7 Seals
- Angelic Prism
- Angry Fly
- Big Chubby
- Bird Cage
- Blood Puppy
- Bob's Brain
- Bum Friend
- Cain's Other Eye
- Cube Baby
- Daddy Longlegs
- Dark Bum
- Dead Bird
- GB Bug
- Guppy's Hair Ball
- Jaw Bone
- Key Bum
- Lil Gurdy
- Lil Haunt
- Little Chubby
- Multidimensional Baby
- Obsessed Fan
- Orbital familiars
- Papa Fly
- The Peeper
- Pointy Rib
- Samson's Chains
- Sissy Longlegs
- Smart Fly
- Spider Mod
- Super Bum
- Temporary familiars
- Worm Friend
- YO LISTEN!
- Isaac's Heart: Isaac can fire tears and leave King Baby and the heart behind, and run into a group of enemies without being damaged.
- BFFS!: Increases King Baby's size. No other effect.
- Duct Tape: King Baby will stay in place relative to Isaac until Isaac starts firing tears. Then King Baby will remain stationary until Isaac has stopped firing and will rapidly move back to him.
- Gemini: Suture will rest near King Baby as long as there are no enemies near Isaac. When Isaac gets near enemies, Suture will rapidly snap from King Baby toward the enemy. Functionally, King Baby has no real effect on Gemini.
- Visually, this can result in the umbilical between Isaac and Suture getting stretched to a long length.
- Friendship Necklace: Familiars will orbit King Baby at all times instead of Isaac, even while not firing. King Baby itself is unaffected.
- RC Remote: Overrides King Baby's halting; familiars will mimic Isaac's movements even while firing. King Baby's auto-targeting remains active.
- King Baby references the official Binding of Isaac tarot card set, in which ??? represents the Emperor.
- The Steam achievement description for unlocking King Baby says "Unlocked a new co-player baby," despite it being an item.
- Before Repentance, King Baby's pickup quote was "Lord of the dead!".
- King Baby's Repentance quote is a reference to Army of Darkness
|??? (Character) Unlocks|
|The Binding of Isaac: Rebirth|
|Achievements||Attributes||Bosses||Cards and Runes||Challenges||Chapters|