Upon use, Isaac farts and knocks back nearby enemies.
Projectiles are also deflected.
Enemies pushed into walls or obstacles take 10 + 2 * (floor - 1) damage.
The deflected projectiles deal 6 damage if they would've hurt Isaac for half a heart, and 7 for a full heart.
Notes
If Isaac swaps Butter Bean for a different active item, then picks up Butter Bean again, it has a 10% chance to transform into Wait What?.
When a run is started, the game has a 5% chance to replace Butter Bean with Wait What? in item pools. Both items are generally not available in the same run.
Synergies
Bird's Eye/Ghost Pepper: Shoots a flame behind Isaac upon each use of Butter Bean. Two flames will be shot if Isaac also has Car Battery.
Book of Virtues: Spawns white wisps on the inner ring. The wisps do not shoot tears, have only 1 health each, release farts that knockback upon death, and cannot be carried across rooms.
Panic Button: Activates Butter Bean upon taking damage. If the damage was from a projectile that Butter Bean can knock away, it will be negated.
Projectiles are also deflected.
Enemies pushed into walls or obstacles take 
If Isaac swaps Butter Bean for a different active item, then picks up Butter Bean again, it has a 10% chance to transform into 
Wait What?.
Bird's Eye/
Ghost Pepper: Shoots a flame behind Isaac upon each use of Butter Bean. Two flames will be shot if Isaac also has 
Car Battery.
Book of Virtues: Spawns white wisps on the inner ring. The wisps do not shoot tears, have only 1 health each, release farts that knockback upon death, and cannot be carried across rooms.
Panic Button: Activates Butter Bean upon taking damage. If the damage was from a projectile that Butter Bean can knock away, it will be negated.
3DS The icon of Butter Bean as seen on the lower 3DS screen.
Beans 
The Binding of Isaac: Rebirth
