Whenever Slave 1 damages a unit, put 1 captivity counter on that unit.
Slave 1 gets Double Damage when attacking a unit with 1 or more captivity counters on it.
Pay 1 Force Absorb 1
Keywords
Double Damage
Double Damage: An isolated, static ability played during the damage placement POP that means, "Put 1 additional damage counter on the defending unit for each 1 damage that wasn't prevented." Damage counters placed by a unit with Double Damage are in addition to the counters that would be placed normally if the attacking unit did not have Double Damage.
Absorb
Absorb X: An activated ability that means, "Prevent up to X damage to this unit, and it gains power for its next attack equal to the amount of damage prevented this way."