I don't actually know anything about Thralls or Kostchtchie, but this inspired me:
Prerequisites: evil, rage, proficiency with warhammer
|2||3||0||0||2||cold be hand|
|3||3||1||1||3||rage +2 str|
|4||4||1||1||4||cold be heart|
|6||5||2||2||6||cold be bone|
|7||5||2||2||7||rage +2 con|
|8||6||2||2||8||cold be sleep|
|10||7||3||3||10||in the black wind|
Class skills: Climb , Intimidate, Jump, Knowledge (religion), Survival, Swim
rage +1/day: rage once more than you already could
cold be hand: all your melee attacks to an additional 1d6 cold damage, and count as magic and evil for overcoming dr
rage +2 str: when you rage, increase your strength by 2 more than you already would
cold be heart: You may use abilities requiring concentration while raging. Also, you are incapable of genuine love or friendship, making you immune to charm effects.
cold be bone: immunity to cold
cold be sleep: Death begins to seep into your body. Like an undead, you are immune to poison and precision damage.
in the black wind: Gain a breath weapon: 15' cone of cold. Usable 3/hour. Does 5d6 damage. Reflex for half, dc 15+con mod.