Benighted Cain and Abel is an unlockable character in Benighted Soul, a mod for The Binding of Isaac.

Cain:
Portable Farm (Consumable slot)
Falsehood of Abel (Finishing Graze! required)

Abel:
Goatify (Consumable slot)
Falsehood of Cain (Finishing Graze! required)

Touch together to switch Main / Second character (with short invincibility).

No switch over 28 seconds hurts Second for 1.5 hearts damage (no penalty).

Holding the map key stops Main.
Holding the drop key stops Second.

Second ignores most damage and goes through obstacles, while move and shoot controls are reversed.

When dying, if either survives, transforms into a ghost player.
(It means that they won't die at the same time like Jacob and Esau, and can even revive after Boss Room)

Specially, they are not bound together forcibly.
They will keep their features even transformed into other characters by some effects.
(Their relationship is more like Strawman, not Jacob and Esau)

Obviously, if you want to get their completion marks, you should not transform both of them.

Play as Cain / Tainted Cain, sacrifice for 12 times to gain Re-death, and then use Re-death in the graveyard of Dark Room to unlock.

The following special synergies and interactions for Benighted Cain and Abel have been documented.

* Note that not all possible synergies and interactions are listed here.

• Download Benighted Soul from the Steam Workshop.