Card sounds may differ from in-game as they get updated.
Killer - A unit with Killer can make one special attack directly against an enemy unit. This can be done the turn it's played, and can target any unit, regardless of Flying, Aegis, or other special abilities.
Tribute - Cards with Tribute have an additional effect when played if a unit went to your void this turn. This includes units that die or units you discard from your hand and deck.