Doomsphere

Unearth. Ward 3. Cannot be tapped.
When Doomsphere enters the battlefield, fateseal
X, where X is Doomsphere's power.
Animate Dead--{b}{b}{b}: Return target creature
from any graveyard, whose power is less than Doomsphere's power, onto the battlefield under
your control.
Melf's Acid Arrow--{u}{b}{x}: Target creature gets
-x/-x, until end of turn.