Mimic Gun

Mimic Gun is a gun that has a 0.1% chance to replace any gun. The Mimic Gun's piercing bullets turn enemy projectiles that they pass through into jammed projectiles that deal a full heart of damage.

After picking it up, the player will not be able to switch to other guns or drop the Mimic Gun until they pick up ammo or deal enough damage, after which the original gun will reappear.

Intentionally fully depleting the ammo will cause the ammo to be refilled to full. It doesn't reveal secret rooms.

Trivia

 * The Mimic Gun's bullets resemble the arcade character Pac-Man.