Jar of Flies is an active item in The Binding of Isaac, added in the Afterbirth DLC.

While heldKilling an enemy adds a fly to the jar that can hold up to 20 flies at once.

On useReleases Blue Flies equal to the number of flies in the jar.

Kills made by Blue Flies, locusts and shooting familiars do not add flies to the jar.

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

This item contributes towards the Beelzebub transformation. Collecting 3 items from this set will grant Isaac flight, converts small enemy flies into Blue Flies, and permanently charms larger enemy flies.

Jar of Flies can be found in the following item pools:

The following tags are applied to this item:

The following special synergies and interactions for Jar of Flies 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.

Jar of Flies

• Adds a blue fly to the jar for each enemy kill
• Maximum of 20 flies can be stored
• Using the jar releases all flies
• Abyss: x1 locust 1x Isaac's damage
• Book of Virtues: x1 middle wisp - 2 hp - 3 damage
• Book of Virtues: Wisps are spawned instead of flies
• Book of Virtues: Up to 5 flies are converted to a wisp with increasing damage

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