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.
Resilience
Resilience X: A cumulative, static ability that means, "As long as this unit has at least X damage counters on it, it gets +X power."