Keen Smell. The tiger has advantage on Wisdom (Perception) checks that rely on smell.

winter killer. in winter the yule cats attacks deal an extra die of damage 

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 13 (3d6 + 4) piercing damage+ 9 (1d10+4) cold damage 

Claw. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 11 (2d8 + 3) slashing damage.

cold gaze. the yule cat targets one creature that it can see and it must succeed on a dc 15 constitution saving throw or take 18 (4d8+2) cold damage and suffer 1 level of exhaustion.