Used Diaper is a trinket in The Binding of Isaac, added in the Afterbirth+ DLC.

Grants a 33% chance to trigger the Skatole effect in each room, making certain fly enemies harmless or less dangerous.

The chance for this to occur is seeded per room.

Spawns a Blue Fly when entering a hostile room.

This page shows the latest information as of the new Repentance+ (Online Co-op) DLC.
To see information about this trinket for the previous Repentance version, check this page instead.

The following special synergies and interactions for Used Diaper have been documented.

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

Below is the Internal Item Description as shown in-game.
Note that some stat changes are not displayed here. Please see the main description for the full effects.

Used Diaper

• 33% chance to gain the Skatole effect for the room
• Spawn a blue fly when entering a new combat room
• Golden Trinket (without Mom's Box): Spawn 2 blue flies when entering a new combat room
• Mom's Box: Spawn 2 blue flies when entering a new combat room
• Mom's Box + Golden Trinket: Spawn 3 blue flies when entering a new combat room

• Check out the trinket description on the external Isaac Wiki.