Olivia, Mobilized for War - 248 M SOI

Flying
Whenever another creature you control enters, you may discard a card. If you do, put a +1/+1 counter on that creature, it gains haste until end of turn, and it becomes a Vampire in addition to its other types.

mythic
Legendary Creature — Vampire Knight
From the Magic: The Gathering set Shadows over Innistrad.