Rylai, the Crystal Maiden

Instant and sorcery spells you cast cost {1} less to
cast.
Activated abilities from creatures you control cost {1} less to activate.
{2}{u}{u}, {t}: Tap target creature an opponent
controls. It doesn't untap during its controler's
next untap step.
{5}{w}{w}{u}, {t}: Destroy all creatures your
opponents control.