Avrad, Mage of Horrid Dreams

Hexproof, fear
{u/b}, {t}: Put a Startle counter on target creature.
Creatures with startle counters on them do not untap during their controller's untap steps.
Nocturnal - At the beginning of your end step, if Avrad, Mage of Horrid Dreams is untapped, destroy all creatures with Startle counters on
them.