Expertise. Ymir's proficiency bonus is doubled for any ability check it makes that uses either of the chosen proficiencies.

Jack of All Trades. Ymir can add half its proficiency bonus to any ability check it makes that uses a skill but doesn’t already include its proficiency bonus

Evasion. Because of extraordinary good luck, Ymir is skilled at avoiding certain dangers. When the he is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it failed. He doesn’t benefit from this feature while incapacitated.

Inspiring Help. Ymir’s assistance becomes especially inspiring. When the sidekick uses its Helpful bonus action, the creature who receives the help also gains a 1d6 bonus to the d20 roll. If that roll is an attack roll, the creature can forgo adding the bonus to it, and then if the attack hits, the creature can add the bonus to the attack’s damage roll against one target.

Reliable Skill.  Ymir has refined its skills to an exceptional degree. Whenever the sidekick makes an ability check that includes its whole proficiency bonus, it can treat a d20 roll of 9 or lower as a 10.

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.

Extra Attack. Ymir may bite twice with it's action. 

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 7 (2d4 + 4) piercing damage. If the target is a creature, it must succeed on a DC 11 Strength saving throw or be knocked prone.

Bonus Actions

 Helpful/Cunning Action. Ymir can use the Help, Dash, Disengage, or Hide actions as Bonus Actions