Kyurem, the Boundary

Glaciate — Creatures you don't control don't
untap during their controller's untap step unless
its controller pays {1} for each creature.
During your upkeep, if you both own and
control all relevant creatures you may choose one:
• Exile Kyurem and Reshiram, Vast White, then
meld them into White Kyurem, Dragon of Truth.
• Exile Kyurem and Zekrom, Deep Black, then
meld them into Black Kyurem, Dragon of Ideals.