Skills: 8
Listen +2, Spot +2, Survival +4? (Note they'll get a +4 racial bonus for tracking by scent as well)
Multiattack sounds good, as does Track as a bonus feat. For the remaining feat, Skill Focus (Survival)? Weapon Focus (hoof)? Power Attack?
Sorry for the delay.
Where's this racial bonus from? Most creatures with scent don't have it, just wolves and the like.
If it's like a regular Unicorn it'll get a +3 circumstance bonus to all Survival checks in its own terrain so I wouldn't give it a racial Track-by-scent as well.
My first idea for the other feat was SF (Survival) simply because it was an SRD Unicorn feat.
That and its impressive Wisdom means it doesn't really need any points in Survival, so I'd divide its skill ranks between Hide, Listen and Spot.
Something like:
Feats: Multiattack, Skill Focus (Survival), Track (B)
Skills: Hide 2, Jump 0, Listen 3, Move Silently 0, Spot 0, Survival 0
Skills: Hide +1* (+5 in cold terrain, +9 immobile in cold terrain), Jump +17, Listen +8, Move Silently +7, Spot +8, Survival +8 (+11 in cold terrain)