Frostwalk Bastion

{t}: Add {c}.
{s}: Until end of turn, Frostwalk Bastion
becomes a 2/3 Construct artifact creature. It's
still a land. ({s} can be paid with one mana from
a snow source.)
Whenever Frostwalk Bastion deals combat
damage to a creature, tap that creature and it
doesn't untap during its controller's next untap
step.