In case you don't know what it is,The binding of isaac repentance is an official DLC,which antibirth,but packed with a ton of new content! Even more secret stuff like never before!
This DLC also includes an item,called Birthright. This item can give a character a unique effect! If a DDLC Character had it,Birthright will can also buff their transformations in certain ways. But here's what I got:
Monika:Adds a chance to spawn a random item next to her upon entering a new floor.
Just Monika:Monika will automatically reroll an active item she spawns into a passive item.

Yuri:Adds a chance to shoot a homing tear the penetrates enemies
Yandere:Yuri will always throw her knife whenever she reaches full charge,but the knife will never come back,so a new one is generated.

Natsuki:Whenever she enters a new floor
Play with me!:Whenever she takes damage,she'll unleash a burst around herself,

Sayori:Whenever she takes damage,she creates a puddle of damaging creep under herself.
Sayo-nara:Adds a chance to spawn a wisp for clearing room.

https://bindingofisaacrebirth.gamepedia.com/Binding_of_Isaac:_Rebirth_Wiki
Here's link for the wiki that includes content for Repentance. But be careful,this also contains spoilers,so I don't know if wanna overlook on it or not,but here it is! Save yourself. ;)