Michiko, Heartbeat Stealer

{t}: Choose up to two target creatures you don't
control. Put a mark counter on each of those
creatures. Michiko, Heartbeat Stealer doesn't untap
during your untap step as long as a creature chosen
this way has a mark counter on it. Activate only
during your turn.

Whenever one or more creatures attack, you may
untap Michiko. If you do, destroy each attacking creature with a mark counter on it, then remove all
mark counters from each creature.