Corruption. If the külmking moves through another creature, it can use a bonus action to corrupt that creature's soul. The target creature must make a DC 16 Charisma saving throw. A creature paralyzed by the külmking has disadvantage on this saving throw. On a failed save, a creature suffers from terrible and violent thoughts and tendencies. Over the course of 2d4 days, its alignment shifts to chaotic evil. A creature that dies during this time, or after this shift is complete, rises 24 hours later as a külmking. The corruption can be reversed by a remove curse spell or similar magic used before the creature's death. On a success, a creature is immune to the külmking's Corruption for the next 24 hours.

Incorporeal Movement. The külmking can pass through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Trampling Charge. If the külmking moves at least 20 feet straight toward a creature and then hits it with a hooves attack on the same turn, that target must succeed on a DC 16 Strength saving throw or be knocked prone. If the target is prone, the külmking can make one hooves attack against it as a bonus action.