A dire wolf grown huge and cold-touched from decades working the pass alone. He doesn't stand and trade blows — he works the field: picking off whoever's nearest early, burying the whole area in a blizzard once he's hurt, and finally bringing the mountainside down between himself and whoever's winning.
A frost bite and a slow on whoever's nearest right now — 2d8+4 cold damage, and a failed Fortitude save (DC 17) halves their speed for three rounds. The mark moves with the strike, not a lingering debuff parked on one target.
A standing blizzard around him that never turns back off once it starts — 1d4 cold damage and a chance to fight at −2 to hit to anyone within 6 meters, reapplied every round.
A moment's warning as the slope starts to groan, then the pass itself blocks the field: a real rubble wall lands between him and whoever's closest, knockdown damage hits everyone nearby, and he comes out of the rubble wearing it — permanent +2 natural armor for the rest of the fight.
Revised CR7 → CR9 after checking Desolate Pass's ambient table: real content there tops out at CR7 (Bugbear Shaman), so the original CR7 boss was merely tying the toughest regular encounter in his own territory instead of clearly exceeding it. CR9 gives him real headroom above the pass's actual wildlife and raiders.
Str 24 and a 1.2× hp multiplier make him hit like the biggest thing in the pass, but Int 4 and no ranks outside Listen/Spot keep him a beast, not a tactician — his threat comes entirely from the script gimmick, not a smart AI. Whiteout is the module's first standing effect that sticks for the rest of the fight once triggered, and Avalanche is the first boss trick to place a real, persistent obstacle on the battlefield instead of just a damage zone.