Birthright

Birthright is an unlockable passive item added in The Binding of Isaac: Repentance.

Effects

Grants a passive ability that varies from character to character. The effect typically enhances/magnifies the character's special traits or helps mitigate some of their downsides.

Character	Pickup Quote	Effect
Isaac	More options	All new item pedestals cycle between two options. Previously-seen items are unaffected.
Tainted Isaac	Inventory up	Allows up to 12 passive items to be carried at a time. Does not consume a slot itself.
Magdalene	Limit breaker + HP up	Adds 1 full Red Heart container. Increases the maximum heart limit to 18.
Tainted Magdalene	HP up!	Adds 1 full red Heart Container. Increases the number of non-draining hearts to 3.
Cain	Better arcades + luck up	+1 Luck. Every floor, except for ???, Chest, Dark Room, The Void, and Home, has a very high chance to contain an upgraded Arcade that generally contains more Machines. This includes odd-numbered floors, Cathedral, and Sheol. Arcades will appear even if Cain is not holding at least 5 Coins. Arcades will still not spawn in Greed Mode.
Tainted Cain	Salvage	The amount of pickups dropped from collecting an item is doubled.
Judas	Belial incarnate	The Book of Belial becomes a passive item that can be held beneath other active items, similar to Book of Virtues. May stack with Book of Virtues. If Judas is not currently holding The Book of Belial, he receives it. The damage boost received from The Book of Belial scales with the amount of charges the active item above it has; may not work with one-time-use items, items with unlimited use, timed recharges, or items that do not follow normal room charge rules (Isaac's Tears, etc). Has special interactions with certain items — see The Book of Belial for more information.
Black Judas	Belial incarnate
Tainted Judas	Extended darkness	Increases the range in which Dark Arts hits enemies and tears.
???	Stronger spirit	Doubles the amount of Soul Hearts gained from HP up items.
Tainted ???	Poop up	Increases the maximum number of poop pickups that can be carried to 29.
Eve	Forever cursed	Whore of Babylon is active regardless of health and Dead Bird is active without taking damage.
Tainted Eve	Coagulate	Red Heart Clots now spawn temporary Half Red Hearts on death that last for two seconds before disappearing. Clots spawned from other types of hearts will not drop hearts.
Samson	Rage up	Bloody Lust can grant 4 more Damage boosts at +0.2 intervals, for a new maximum total of +14.0.
Tainted Samson	Unstoppable force	The berserk timer gains 3 seconds instead of 1 when Tainted Samson kills an enemy.
Azazel	Wide breath	Azazel's Brimstone beam becomes much wider like Mega Blast, with 2× larger collision area. No effect on damage.
Tainted Azazel	Stronger sneeze	Doubles the size of Tainted Azazel's Hemoptysis sneeze attack.
Lazarus	Come back stronger	No direct effect. The item is triggered if Lazarus dies and becomes Lazarus Risen.
Lazarus Risen	Temporary DMG up	Grants a +7.2 Damage bonus that fades by 0.12 per second. Until the effect completely fades, killing an enemy restores 0.07 damage to the bonus.
Tainted Lazarus	Superposition	The non-active form of Tainted Lazarus will appear in ghostly form, being completely immune to damage and dealing 25% damage (including tear effects such as Holy Light). Holding down the "drop" key allows the active form to move independently of the other form, similar to Jacob and Esau. Using Flip will cause the two characters to switch states while maintaining positions. Both characters receive the Birthright effect when one character collects it.
Dead Tainted Lazarus	Superposition
Eden	???	Creates 3 random items from random item pools. Only one can be taken. Ignores item weight and can spawn items that have already been taken during the run. Can also spawn multiples of the same item, if they exist in multiple item pools.
Tainted Eden	Eternal	Items gained before Birthright will not be re-rolled, neither by taking damage, nor by items such as D4 and Missing No.. Items gained afterwards will still be affected.
The Lost	Better destiny	Prevents items with the `nolostbr` item tag from appearing. This automatically re-rolls most items that aren't beneficial to The Lost, namely ones that only give health, flight, and/or spectral tears or activate upon taking damage.
Tainted Lost	Extra life	Grants an extra life that revives Tainted Lost in the same room and deals 200 damage to nearby enemies. It can hit the same enemy up to 4 times.
Lilith	Offensive Formation	Most familiars that normally follow Lilith, including Lilith's innate Incubus, will always be positioned in front of Lilith, creating a stack, facing whatever direction she was shooting. Non-attacking familiars (The Relic, Farting Baby, etc.) will follow Lilith's most recently acquired attacking familiar instead; if the most recent familiar is throwable like Holy Water, familiars following it will also be launched with it. If Lilith has King Baby, it will always be positioned directly in front of Lilith with all other affected familiars forming a semi-circle around it, and will behave normally otherwise. Dry Baby is considered an "attacking familiar" and will be within the stack. Lil Portal and Jaw Bone are exempt and behave normally.
Tainted Lilith	Conjoined	Familiars that normally follow Tainted Lilith will instead act like and stack on top of her Gello familiar, disappearing inside of her while she's not firing and swinging out when she attacks. The melee attack gains a flat +3 damage bonus per familiar (regardless of damage multipliers) and if those familiars can shoot, they do so along with the Gello familiar. The Gello familiar gains the properties of King Baby, causing attached familiars to automatically aim and shoot at enemies. Familiars like Jaw Bone or Holy Water still function, but they are bound to the Gello familiar rather than their normal means of movement.
Keeper	Coin up	Adds one Coin Heart and raises Keeper's maximum Coin Heart limit to 4.
Tainted Keeper	Money money money	Strongly attracts the coins dropped by killed enemies from a short distance. No effect on other coins.
Apollyon	Regurgitate	Using Void has a 10% chance to spawn one previously destroyed passive item (while keeping the bonus stats). Each absorbed passive item has an equal chance to be spawned. Spawned items can be spawned again even if they are not reabsorbed. Absorbing duplicates of the same item will make it more likely to be spawned, as each duplicate counts as a separate item and thus has its own chance to be spawned. Birthright has no effect if Void is not held.
Tainted Apollyon	Torment	Holding down the fire button causes Abyss locusts to continuously damage enemies instead of returning.
The Forgotten	Unchained	The Soul is unchained and free to move. It can move to different rooms, leaving The Forgotten behind, and switching back teleports The Soul back to The Forgotten.
Tainted Forgotten	Recall	Tainted Soul is given Recall, an unlimited-use active item, in their pocket active slot. When used, Recall pulls Tainted Forgotten into Tainted Soul's hands automatically from a distance, dealing damage to enemies as it travels.
Bethany	Conserve your faith	Activating an item using Soul Charges is free 50% of the time.
Tainted Bethany	Artifact	Spawns four Lemegeton wisps of items with a quality of 3 or higher. These wisps are much larger and have much higher HP than normal wisps.
Jacob and Esau	What's yours is mine	The character who picks up Birthright gains copies of the three most recent passive items from the other.
Tainted Jacob	It's not yours	Dark Esau splits into two. Both Esaus will always charge at the same time, and one will not charge if the other is not in position. Using Anima Sola chains both Dark Esaus at once and forces them together into one spot. Subsequent uses release each Dark Esau one at a time. Anima Sola's recharge time is reduced to 10 seconds, and chain duration is increased to 6.67 seconds.

Notes

Birthright effects are stackable when playing as Tainted Lost and Tainted Bethany.
Each additional copy of Birthright for Magdalene, Tainted Magdalene, and Keeper will add another heart container; however, their respective health caps will not be raised any further. Cain will also gain +1 Luck for each copy of Birthright.
When Magdalene or Keeper enter the area in which Knife Piece 2 can be acquired, all hearts above the usual cap are removed and are not restored upon leaving the area. Additional hearts can be regained afterwards.
While playing as Tainted Cain in Greed Mode, purchasing an on-sale item over and over while having Birthright results in almost infinite consumables.
If The Soul enters a new floor with Birthright, swapping back to The Forgotten will cause him to appear at The Soul's current location.

Interactions

Sacrificial Altar + Tainted Eve: Clots won't drop half red hearts after getting sacrificed.

The following familiars are unaffected by Lilith's and Tainted Lilith's Birthrights:

All orbitals
Damage-triggered familiars (Dead Bird, etc.)
Bouncing familiars (BBF, etc.)
Wandering familiars (Spider Mod, etc.)
Mimicking familiars (Papa Fly, etc.)
All familiars spawned by active items as Monster Manual
Abel
Angry Fly
Blood Puppy
Bumbo
Bum Friend
Daddy Longlegs
Dark Bum
Finger!
Found Soul
Fruity Plum
Gemini
Guppy's Hairball
Isaac's Heart
Key Bum
Lil Gurdy
Lil Haunt
Lost Soul
Pointy Rib
Quints
Robo-Baby 2.0
Samson's Chains
Star of Bethlehem
Twisted Pair
Worm Friend

In-game footage

Trivia

Birthright is from the Antibirth mod.
- Before Antibirth the item originated from the Binding of Isaac: Community Remix mod, where it was known as 'Soul Script'.
This item's name, description, and unlock requirement are a reference to the biblical story of Jacob and Esau, in which Esau trades his birthrights to Jacob in exchange for stew.
- When Tainted Jacob picks up Birthright, Dark Esau, a representation of his own rage, seemingly becomes only angrier and doubles in power.
  - Birthright's effect doubling Dark Esau's power, instead of Tainted Jacob's, and the quote "it's not yours", further reflects the fact that it was originally his.
Prior to patch V1.7.6, Tainted Jacob's Birthright pickup quote was "There is no escape".
Tainted Keeper's pickup quote could be based off the song Money, Money, Money, by the band ABBA.
Eden's Birthright could be a reference to how Eden functions in the card game The Binding of Isaac: Four Souls, as Eden starts the game by drawing 3 treasure cards and selecting one to keep permanently while the other two are discarded.

Bugs

Bug!	Playing as Keeper, having more than 3 HP, and entering the area in which Knife Piece 2 can be acquired will remove the fourth HP (can be increased back to 4 HP after)

Bug!	Playing as Magdalene, having more than 12 hearts, and entering the area in which Knife Piece 2 can be acquired will completely remove all hearts above 12.

Bug!	Playing as Tainted Lazarus, Picking up Birthright and using Flip at the same time as the other form appears will cause the other form to be in a bugged state where he acts significantly faster than intended. Restarting the game will undo the effects.