Reckless. At the start of his turn, Ymir can gain advantage on all melee weapon attack rolls during that turn, but attack rolls against him have advantage until the start of his next turn.

Danger Sense. Ymir Frostwalker has advantage on DEX saving throws against effects that he can see while not blinded, deafened, or incapacitated.

Elemental Cleaver. While raging, Ymir's greataxe deals cold damage, and it deals an extra 4 (1d6) cold damage when it hits. It also gains the thrown property (range 20/60), reappearing in his hand the instant after it hits or misses a target (included in the attack).

Multiattack. Ymir Frostwalker makes two greataxe attacks.

Greataxe. Melee or Ranged Weapon Attack: +9 to hit, reach 10 ft. or range 20/60 ft., one target. Hit: 12 (1d12 + 5) slashing damage plus an additional 4 (1d6) cold damage. 

Giant's Havoc. Once per turn, when Ymir hits a target with a melee weapon attack or a ranged weapon attack using a thrown weapon, he can imbue the attack with an additional effect:

Stone Strike. The target takes an extra 4 (1d6) force damage and must succeed on a Strength saving throw (DC 17) or be pushed 10 feet from him in a straight line.

Frost Strike. The target takes an extra 4 (1d6) cold damage and must succeed on a Constitution saving throw (DC 17) or its speed is reduced to 0 until the start of his next turn.

Battle Rage (Recharge 4-6). Ymir Frostwalker enters a state of primal ferocity for 1 minute or until he falls unconscious or hasn't attacked or been attacked before the end of his next turn. Whil in this state, he has resistance to bludgeoning, piercing, and slashing damage.

Frigid Retaliation (Recharge 5-6). Immediately after a creature Ymir can see within 30 ft. of him hits him with an attack roll and deals damage, he can retaliate with a conjured blast of ice. The creature must make a Constitution saving throw (DC 17). On a failed save, the creature takes 10 (1d8 + 4) cold damage, and its speed is reduced to 0 until the end of its next turn.

Stone’s Endurance (Recharge 5-6). When Ymir takes damage, he can use his reaction to reduce the damage taken by 11 (1d12+4).