Corvia, the Avenging Strike

You may choose not to untap Corvia during your
untap step. If you do, remove a -1/-1 counter
from her.
{4}{r}{g}, {t}: Until end of turn, whenever a source
you don't control would deal damage to you or a
permanent you control, prevent that damage and
Corvia deals that much damage to the source's
controller. Put a -1/-1 counter on Corvia.