Swallowed M80 is an unlockable trinket in The Binding of Isaac, added in the Repentance DLC.

Isaac has a 50% chance to explode upon taking damage, and deal 185 damage to nearby enemies.

The explosion uses Isaac's bomb synergies.

The explosion can also trigger when playing Blood Donation Machines, Devil Beggars, etc, destroying them in the process.

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.

Defeat Mother as Tainted Samson.

Swallowed M80 can be found in the following item pools:

The following special synergies and interactions for Swallowed M80 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.

Swallowed M80

• 50% chance for Isaac to explode when taking damage
• Golden Trinket (without Mom's Box): 100% chance for Isaac to explode when taking damage
• Mom's Box: 100% chance for Isaac to explode when taking damage
• Mom's Box + Golden Trinket: 100% chance for Isaac to explode when taking damage

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