Ranni the Witch

When Ranni enters the battlefield or deals combat damage
to a player, you may Discover X, where X is your devotion to Blue. (Exile cards from the top of your library until you exile a nonland card with that mana value or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom of your library in a random order.)

Assassin creatures you have in your graveyard have Flashback. Their Flashback cost is equal to their mana cost.

{1}{b}{b},{t}: Exile a creatu