({S} can be paid with one mana from a snow source.)

Whenever Marit Lage's Slumber or another snow permanent enters the battlefield under your control, scry 1. At the beginning of your upkeep, if you control ten or more snow permanents, sacrifice Marit Lage's Slumber. If you do, create Marit Lage, a legendary 20/20 black Avatar creature token with flying and indestructible.

({T}: Add {B}.)

Whenever another snow permanent enters the battlefield under your control, you may have target player mill two cards.

Enchant creature Enchanted creature gets +2/+1 and has "{S}: This creature can't be blocked this turn except by snow creatures." ({S} can be paid with one mana from a snow source.)

Enchant creature When Winter's Rest enters the battlefield, tap enchanted creature. As long as you control another snow permanent, enchanted creature doesn't untap during its controller's untap step.