Isaac has a 50% chance to explode when he takes damage, similarly to if he used Kamikaze!.
The explosion deals 185 damage and uses most of Isaac's bomb synergies.
The explosion does not cause additional damage to Isaac.
Notes
Causes Devil Beggar and Hell Game to become essentially unplayable, as any damage that could trigger Swallowed M80 will likely cause Isaac to explode, killing them.
Causes Blood Donation Machines and Confessionals to act as if they were destroyed from the explosion despite surviving and functioning normally, resulting in extra coin and Heart drops.
Golden Trinket / Mom's Box / Swallowed M80: Having either of these effects/another copy of the trinket raises the chance to trigger an explosion to 100%.
Pyromaniac: Heals half a red heart on triggered explosion, rendering Isaac invincible on earlier stages if combined with the above synergy.
Interactions
Tainted Magdalene: Explosions will kill enemies before Tainted Magdalene's “hug” attack, preventing heart drops from killing enemies on contact from being guaranteed.
No Effect
All bomb upgrades affect Swallowed M80 except the following:
Kamikaze!.
Devil Beggar and 
Hell Game to become essentially unplayable, as any damage that could trigger Swallowed M80 will likely cause Isaac to explode, killing them.
Blood Donation Machines and 
Confessionals to act as if they were destroyed from the explosion despite surviving and functioning normally, resulting in extra coin and 
Heart drops.
Curse Room or 
Sacrifice Room spikes.
Golden Trinket / 
Mom's Box / 
Swallowed M80: Having either of these effects/another copy of the trinket raises the chance to trigger an explosion to 100%.
Pyromaniac: Heals half a red heart on triggered explosion, rendering Isaac invincible on earlier stages if combined with the above synergy.
Tainted Magdalene: Explosions will kill enemies before Tainted Magdalene's “hug” attack, preventing heart drops from killing enemies on contact from being guaranteed.
Tainted Samson Unlocks 
Mother Unlocks 
The Binding of Isaac: Rebirth
