Ashiok's Familiar

Flash
Whenever Ashiok's Familiar attacks or blocks,
exile the top card of target player's library. If it's
a creature card with flying, Ashiok's Familiar
gains flying until end of turn. The same is true
for first strike, double strike, deathtouch,
indestructible, lifelink, menace, and trample.
"Your mind is its playground."
— Ashiok, Nightmare Muse