Glayce's Frostbitten Breath

(You may cast a legendary sorcery only if you control
a legendary creature or planeswalker.)
Tap X target creatures. Glayce's Frostbitten
Breath deals X damage to each creature tapped
this way. Those creatures don't untap during
their controller's next untap step.
Centuries ago, a cryomancer sought to glaciate the underworld.