Nix, Winter Witch

{s}{s}, {t}: Nix, Winter Witch becomes a copy of
target creature until end of turn, except its name
is still Nix, Winter Witch, it's legendary and
snow in addition to its other types, and it has "Whenever you cast a noncreature spell, untap
this creature."
At the beginning of your upkeep, if you control
five or more snow permanents, you may pay {u}{r}{g}, exile Nix, then return them to the battlefield transformed under their owner's
control.