Not to be confused with the Mulligan monster

A blue fly with a blue heart above it.


A 1/6 chance to spawn an Attack Fly when Isaac damages an enemy. Unlike Guppy, most familiars do not contribute to the spawning of Attack Flies, though Attack Fly attacks can spawn more Attack Flies.

Regardless of how many Flies are spawned, no more than five will follow Isaac into the next room.


Brimstone, Mom's Knife and other nontraditional tear effects can spawn Flies when making contact with enemies.

It is not possible to spawn two Flies per hit while Guppy.


  • Soy Milk - The high fire rate and low damage can allow massive numbers of flies to spawn by continuously attacking a single enemy.
  • Inner Eye and Mutant Spider - Can spawn multiple Flies with one attack.
  • Technology 2 - Has a much higher chance of spawning Flies, due to Technology 2's high fire rate.


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