Vystur, the Oathbreaker

Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Frost Aura. Frost crystallizes the air around the giant up to 10 feet away. When a creature enters the area for the first time or starts its turn there, it takes 3 (1d6) cold damage, has it’s movement halved, and it has disadvantage on it's next attack roll.

Multiattack. The giant makes two greatsword attacks.

Greatsword.  Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 13 (2d6 + 6) slashing damage plus 4 (1d6) cold damage.

Fling. The giant attempts to throw a Small or Medium creature within 10 feet of it. The target must succeed on a DC 16 Dexterity saving throw or be hurled up to 60 feet horizontally in a direction of the giant's choice and land prone, taking 1d8 bludgeoning damage for every 10 feet it was thrown.

Smash. Melee Weapon Attack: +9 to hit, reach 10 ft., the giant smashes a creature into the ground for 18 (3d6 + 6) bludgeoning damage. The creature is stunned until the end of it's next turn.

Icy Vengeance. In place of an attack action, the giant may use it's reaction to freeze a creature fleeing it's aura. The creature must succeed on a constitution saving throw (DC 12) or become grappled by the ice around it.