???, also known as the Blue Baby, is a character unlocked by defeating Mom's Heart ten times. He starts with three soul hearts, and his health meter is unique in that he cannot gain red Heart Containers. If an item would grant him a red heart container, it adds a soul heart instead.
Abaddon
Increases damage and speed, removes all red heart containers, grants six black hearts, and adds a chance to shoot fear tears. costs three Soul Hearts and grants six Black Hearts, damage up, fear shot, and no negative effects to ???. Abaddon can be bought safely regardless of current health, because its price can be deducted from the acquired Black Hearts retroactively.
Ankh
Upon death, the player will respawn as ??? with 3 soul hearts. is effectively a 
1up!
Gives an extra life. Upon death, you will respawn in the previous room with full health and lose the 1up!. for ???.
Athame
Whenever Isaac takes damage, a black ring briefly appears around Isaac, dealing damage to all nearby enemies. can be used to produce black hearts upon taking damage.- Balls of Steel Pills or The Hierophant grant two soul hearts, both of which are more useful than normal HP up items.
The XI - Strength card gives ??? a permanent soul heart.
Ceremonial Robes
Adds 3 black hearts and increases Damage by 1. costs three Soul Hearts and grants three Black Hearts and damage up. Like Abaddon, this item is always safe to take.
Crown of Light
Gives Isaac a crown that glows blue when active, and turns gray when inactive. While Isaac has no empty red heart containers, Isaac's tears are replaced with blue diamond tears that deal double damage. Regardless of health, the crown will deactivate for the current room when Isaac takes damage. will always activate.
Daemon's Tail
Most non-specific heart drops become black hearts, but heart drops are significantly less common. replaces useless Red Hearts with Black Hearts.
Dark Bum
Spawns a familiar that follows Isaac around and collects red hearts. For every one-and-a-half red hearts collected, Dark Bum will generate one soul heart, one hostile Spider or one friendly blue spider. converts useless Red Hearts into Soul Hearts and spiders.
Dim Bulb
Provides a boost to all stats when Isaac's active item is completely uncharged. is able to be activated every room due to the single charge on 
The Poop
Spawns a pile of poop where the character is standing and knocks nearby monsters back. May yield pickups like regular poop., providing a consistent stat boost.
Gimpy
Has a chance of spawning a soul heart or black heart when taking damage. Enemies have a chance to drop a Half Red Heart after being killed. has a chance to spawn Soul Hearts when hit.
Lazarus' Rags
Upon dying, resurrect as Revived Lazarus with one heart container and Anemic item. causes ??? to be resurrected as Lazarus Risen when he dies, allowing the gathering of Heart Containers. Once this happens, however, you are no longer playing as ???, and therefore cannot get any of his achievements/unlocks. The same effect happens with the use of 
Judas' Shadow
Adds an extra life; upon death, it respawns Isaac as Black Judas with only two black hearts..
Maw of the Void
+1.0 Damage Up. After continuously firing tears for 2.5 seconds, a red cross appears on Isaac's head that, upon releasing the fire button, creates a black ring that rapidly deals damage equal to Isaac's tear damage to any enemies in contact with it. can produce black hearts.
Midas' Touch
Enemies that touch you are stunned and turn gold. Any enemy killed while in this state will drop a coin. makes The PoopSpawns a pile of poop where the character is standing and knocks nearby monsters back. May yield pickups like regular poop. create golden poop.
Mitre
Grants a chance of converting any red hearts pickups into soul hearts instead. makes soul heart pickups more common.
Monkey Paw
If the character has half a heart after taking damage, it drops a Black Heart. The effect can trigger up to three times, after which the trinket will disappear. will drop 3 Black Hearts, but must take damage for each one to spawn.
Petrified Poop
Greatly increases the chances of a pickup dropping when destroying poop. is useful early on to get more pickups from The Poop every room.
Pyromaniac
Isaac heals 1 heart instead of taking damage from an explosive source. Adds 5 bombs. makes ??? immune to all explosions.
The Polaroid
If the character has half a red heart or no red hearts after taking damage, it triggers the Book Of Shadows effect, creating a shield that nullifies all types of damage for 5 seconds. Also allows entrance into The Chest. and 
The Negative
If the character has half a red heart or no red hearts after taking damage, it triggers The Necronomicon effect, damaging all enemies in the room. Also allows entrance into the Dark Room. always activate when taking damage.
The Relic
Isaac is followed by a small blue cross that will drop a Soul Heart every 4 rooms., which is generally useful, is especially useful to ??? as it spawns Soul Hearts.
Satanic Bible
Upon activation, Isaac gains a black heart. generates Black Hearts.
Serpent's Kiss
Tears now have a random chance to apply a poison effect, causing 4 or 6 damage per tick to enemies (Similar to The Common Cold item). Isaac now deals poison damage on contact with enemies similar to The Virus item (Damage over time 4 or 6 per tick). Enemies that were poisoned have a chance to drop a black heart when killed. can produce black hearts by poisoning enemies.
Squeezy
Increases tears by 0.4, and spawns 2 Soul Hearts pickups. and 
Mr. Dolly
Tears and Range up. Spawns 3 random types of hearts on the floor when picked up. increase ???'s tears and can grant soul hearts.
Whore of Babylon
Increases damage and speed whenever Isaac has half a red heart or less (one red heart for Eve), ignoring any soul or black hearts. is always active.
- Items that directly add Red Hearts to the health bar, such as
Yum Heart
Restores 1 whole red heart. or full health pills, are useless.
- Blood Banks and Devil Beggars are riskier, as they deplete health that is harder to replenish.
- If ??? has only one heart,
Experimental Treatment
Randomly increases and decreases some of the character's stats. There will always be at least one stat increase and one decrease and the same stats can be increased/decreased multiple times. has a chance to be lethal.
Cursed Skull
If Isaac has less than one full red heart after taking damage, he will be immediately teleported to the last cleared room he was in. will automatically teleport ??? out of the room upon taking any damage, as he doesn't have any Red Hearts.
Dead Cat
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. will remove all but one Soul Hearts. However, it can be used as a last resort if you are running very low on Soul Hearts.
Glass Cannon
When used, reduces Isaac's health to half a heart (including soul and black hearts) and fires one large piercing spectral tear that does a lot of damage. The damage done by Glass Cannon scales with Isaac's damage (at base damage it does 45 damage). will bring ??? down to half a soul heart, and not give back any health upon leaving a room due to ???'s lack of red hearts. This item essentially takes away most of the player's health in exchange for a single high damage tear.
Guppy's Paw
Removes one red heart container in exchange for gaining 3 Soul Hearts., since requiring red hearts to convert, would be a useless item to hold (but should still be picked up and swapped back in order to get credit towards the Guppy transformation). Guppy's Paw may still be used to activate the 
Broken Remote
Triggers the Teleport effect whenever an activated item is used..
Judas' Tongue
Items in the Devil Room only cost 1 heart. Soul heart trades still cost 3 Soul hearts. doesn't lower the price of soul heart devil deals.
Little C.H.A.D.
A familiar who will drop a half red heart every 2 rooms. is useless unless paired with Dark BumSpawns a familiar that follows Isaac around and collects red hearts. For every one-and-a-half red hearts collected, Dark Bum will generate one soul heart, one hostile Spider or one friendly blue spider., where it becomes very useful.
- Sleeping on a bed will give ??? three soul hearts.
- Enemies who deal full hearts of damage can be very dangerous in the early floors of the game.
- The PoopSpawns a pile of poop where the character is standing and knocks nearby monsters back. May yield pickups like regular poop. - While not the most useful item, it can allow ??? to cross small gaps by bombing the poop from the opposite side, much like one would for Rocks. Furthermore, in rooms with non-flying enemies that chase the player (with the exception of spiders), the poop can be used in a corner of the room making ??? untouchable, allowing the player to kill them without taking damage (if the player moves away from the pile of poop generated, this will no longer work).
- Bone Hearts grant an empty bone heart upon pickup, but they cannot be refilled using red hearts.
- ??? appears in the original Binding of Isaac.
- ???'s unlock requirements in Rebirth are the same in the original Binding of Isaac.
- The name "Blue Baby" had not appeared in the game itself until the Afterbirth expansion, with a co-op baby named as such.
- ???'s common nickname, Blue Baby, is a reference to blue baby syndrome, in which a baby's skin complexion appears blue from a lack of oxygen in its blood due to a congenital heart defect.
- Many of Edmund's older flash games from Newgrounds feature ??? and
Brother Bobby
Follows Isaac around shooting normal tears.. ??? was Edmund's mascot from 1996-2002.
- In several cutscenes, Isaac is depicted suffocating inside a chest. ??? first appears inside an identical chest, and is the follow up boss after Isaac. Blue skin tone is typically used to show suffocation, and X eyes imply that the character is either knocked out or deceased.
- After death, the bowels of the deceased will loosen, causing them to defecate themselves. This is most likely the reason ??? starts with The PoopSpawns a pile of poop where the character is standing and knocks nearby monsters back. May yield pickups like regular poop..
- Unlike many of the other characters, ??? does not appear in the Bible or any religious scripture.
- The AnkhUpon death, the player will respawn as ??? with 3 soul hearts. will resurrect any character as ???, even before he is unlocked.
- Although "Blue Baby" is considered an unofficial nickname for ???, the character is referred to by this name in the some of the game's code. One example of this is the image file for the character, named
character_006_bluebaby.
The Binding of Isaac: Rebirth 
Achievements
Attributes
Bosses
Cards and Runes
Challenges
Chapters
Characters
Co-op
Items
Item Pools
Monsters
Objects
Pickups
Pills
Rooms
Seeds
Transformations
Trinkets
