Shivara, Night Clan Recruiter

Flash
When Shivara enters, choose one —
•Create two 1/1 back Elf Assassin creature tokens with "{b}{b},{t} Sacrifice this creature: destroy target nonland permanent you don't control."
•Create two 1/1 blue Elf Assassin creature tokens with "{u}{u},{t} Sacrifice this creature: draw a card."

Retreat {u}{u}{b}{b} (Return this creature to its owners hand. You may only activate this ability at a time you could cast a sorcery.)