Based of of the Winterwolf: http://www.d20pfsrd.com/bestiary/monster-listings/magical-beasts/winter-wolf
But modified for advancements as a druid animal companion.
Medium winter wolf - 1st level:
Size Medium; Speed 50 ft.; AC +2 natural armor; Fort +5, Ref +5, Will +1; Attack bite +2 (1d6+1 plus trip); Ability Scores Str 12, Dex 15, Con 14, Int 2, Wis 12, Cha 6; Special Qualities low-light vision, scent, darkvision, fire vulnerability, cold immunity. Feats Skill Focus (Perception)
4th Level Advancement
+2 natural armor; Attack cold bite (plus 1d6 cold); Ability Scores +2 Int, +1 Cha
7th Level Advancement
Size Large; +2 natural armor; Attack bite (1d8); Ability Scores Str +8, Dex –2, Con +4, +3 Int, +1 Cha; Languages: Common
10th Level Advancement
+2 natural armor; Ability Scores +2 Int, +1 Cha; Languages: Common; Special Attacks breath weapon (every 1d4 rounds, 15-ft. cone, 6d6 cold damage, Reflex half DC 17)