Firestarters Torch have suffix -4 spell mana cost. it not work with fire warpath. mana ist decreased
This is because it is -4 SPELL mana cost and warpath even if you convert it from physical to fire skill it is still not a spell - it does not have the spell tag on it, so Firestarter’s Torch is working fine. If you have picked the chance to cast smite node (Winds of Justice) then your smites will be free to cast with it cuz they do have the spell tag.