The Krampus will make the right decision!

The more naughty a Tamer has been, the greater his suffering will be. If you have a Krampus, it won't do you any damage. However, if you don't kill any of them, it will heal you to reward you for being a nice Tamer. If your opponent has never killed anyone, and neither have you, he will heal himself. The more people your opponent kills, the more terrible the damage the Krampus will be.

The Krampus is a legendary creature that only appears at Christmas time. Physically, he is a mix between a goat and a demon. Once unlocked by the tamer, he can be used all year round. Otherwise, you have to wait until the next Christmas to have a chance to see him appear again.