Whenever a unit's Backfire is triggered, that unit gets +1 health until it is discarded.
Each unit gets Backfire 1 (If you roll at least one natural 3 for this unit's attack, this unit does 1 dice of damage to itself when the attack ends.)
Keywords
Backfire
Backfire X: A cumulative ability triggered by the initial dice roll that means, "When you roll at least one natural three with this unit's attack dice before re-roll, this unit does X dice of damage to itself when the attack ends." Backfire applies only to dice rolled for an attack, not to dice rolls for abilities like Retaliate.