Legendary Resistance (3/Day). If Kostchtchie fails a saving throw, he can choose to succeed instead.

Magic Resistance. Kostchtchie has advantage on saving throws against spells and other magical effects.

Innate Spellcasting. Kostchtchie's innate spellcasting ability is Charisma (spell save DC 20). He can innately cast the following spells, requiring no material components:

At will: command, darkness

1/day each: dispel evil and good, gate, harm, telekinesis, teleport, wind walk

Multiattack. Kostchtchie makes two melee attacks, only one of which can be a bite attack.

Bite. Melee Weapon Attack: +18 to hit, reach 5 ft., one creature. Hit:13 (1d6 + 10) piercing damage.

Matalotok (Warhammer). Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit:19 (2d8 + 10) bludgeoning damage, or 21 (2d10 + 10) bludgeoning damage when used with two hands, and the weapon emits a burst of cold that deals 10 (3d6) cold damage to each creature within 30 feet of it.

Attack. Kostchtchie makes one melee weapon attack.

Charge. Kostchtchie moves up to his speed.

Curse (Costs 2 Actions). Kostchtchie curses one creature he can see within 60 feet of him. The cursed creature gains vulnerability to all damage dealt by Kostchtchie until the end of Kostchtchie's next turn.