Darklight Soulstealer

Soul harvest (You may sacrifice any amount of Spirit creatures when you summon this creature. For every Spirit sacrificed this way, reduce this creature's summoning cost by {1} and put a Soul counter on it)
Remove a Soul counter from Darklight Soulstealer: Remove from the game target Spirit from your Graveyard to deal X damage to target creature, where X is the removed Spirit creature's strength.