The Arctic Core's Protection

At the beginning of each opponent's end step,
if you weren't attacked this turn, draw two
cards and gain 3 life.
{1}{w}{u}: Freeze target creature. Activate this ability only once each turn and only as a
sorcery. (Tap that creature, then put a stun counter
on it. For as long as that creature remains tapped, its activated abilities can't be activated.)