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.
Lucky
Lucky X: A cumulative, static ability that means, "Each time this unit attacks or is attacked, you may re-roll up to X of this unit's attack dice or have your opponent re-roll up to X attack dice against this unit." Both players can use Lucky effects according to the rules for POP chances. Lucky is used only once after all triggered re-roll effects resolve. You can't re-roll more dice than are rolled for the attack. You may choose to roll any number of dice up to the Lucky value.