SCP-966, Sleep Killer

Shroud
{u/b}{u/b}{u/b}: Put a Wave counter on target creature.
On each upkeep, if a creature has Wave counters equal to their toughness, you may tap SCP-966,
if you do, destroy that creature. You gain life equal
to it's toughness.
"You feel like something is here with you, but you do
not see anything."