Akali, the Rogue Assassin

Commander Ninjutsu {1}{u}{b}
Assassin's Mark- When Akali, the Rogue Assassin enters the battlefield and at the beginning of your upkeep, place an assassination counter on target creature an opponent controls.
If Akali deals combat damage to a player, you may destroy target creature with an assassination counter on it. If you do, search your library for a permanent with equal or lesser converted mana cost. You may play that card without paying its