Whenever Mission would damage one of your opponent's Characters (after damage prevention), you may draw a card.
As long as Zaalbar is in any arena, Mission gets Stealth.
Keywords
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.
Stealth
Stealth: An isolated, static ability that means, "This unit can't be attacked unless it's tapped or has damage counters on it." An untapped and undamaged unit with Stealth can still be affected by alternative types of damage. (Such as Overkill.) As long as the unit has any number of damage counters on it, it can't use Stealth.