Keen Hearing and Smell. The wolf has advantage on Wisdom (Perception) checks that rely on hearing or smell.

Pack Tactics. The wolf has advantage on attack rolls against a creature if at least one of the wolf's allies is within 5 feet of the creature and the ally isn't incapacitated.

Danger Sense. Beginning at 2nd level, the sidekick has advantage on Dexterity saving throws against effects that it can see, such as traps and spells. This feature doesn’t work if the sidekick is incapacitated.

Improved Critical. Starting at 3rd level, the sidekick’s attack rolls score a critical hit on a roll of 19 or 20 on the d20

Battle Readiness. Ymir has advantage on initiative rolls. 

Indomitable. Starting at 9th level, the sidekick can reroll a saving throw that it fails, but it must use the new roll. When it uses this feature, it can’t use the feature again until it finishes a long rest. The sidekick can use this feature twice between long rests starting at 13th level and three times between long rests starting at 17th level.

Improved Defense. Ac increases by 1 .

Extra Attack. Ymir can make three bite attacks with one action. 

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (2d4 + 3) piercing damage. If the target is a creature, it must succeed on a DC 15 Strength saving throw or be knocked prone.

Second Wind. Starting at 1st level, Ymirk can use a bonus action on its turn to regain hit points equal to 1d10 + its level in this class. Once it uses this feature, it must finish a short or long rest before it can use it again.