Can we just do resistance X positive energy? As for improved turning resistance, I'm not sure if I favor just big turning resistance, immunity to turning, or something unique.
Agreed to those suggestions on the sword. Unique magic item or an inherent property of Maramet?
Rustblade (Su): Any weapon wielded by Maramet takes on a rusted appearance. If Maramet makes a successful touch attack with this weapon aganist a metal object, it causes the target metal to corrode, falling to pieces and becoming useless immediately. This can destroy up to a 10-foot cube of metal instantly. Magic armor and weapons, and other magic items made of metal, must succeed on a DC x Reflex save or be dissolved. The save DC is Charisma-based and includes a +4 racial bonus.