Shirogane Noel, Fair Knight

At the beginning for your upkeep you may detain target creature.(Until your next turn, that
permanent can't attack or block and its activated abilities can't be activated.)
You may exert Shirogane Noel as it attacks.
When you do, pay {x}{w/u}{w/u}, where X is the mana
value of target creature defending player
controls with less power than Shirogane Noel
that is detained, gain control of that creature.
(An exerted creature won't untap during your next
untap step.)