MTG Treachery

Identity — Guardian

Undercover — Unveil this identity only if another player controls ten or more permanents.

Unveil {X}{2}

When The Cryomancer is unveiled, tap X target permanents. If it’s your turn, those permanents don’t untap during their controller’s next untap step.

Illustrated by OPOA @ Pinterest

Card ID: #5

The X in the unveiling triggered ability has the same value as the X paid in the Unveil ability. This is pretty easy to derive since there is no other source of X.

If a permanent affected by The Cryomancer changes controllers before its old controller’s next untap step, The Cryomancer will prevent it from becoming untapped during its new controller’s next untap step.