Simple. Use a Whammy to Corpse Skin it and Onslaught it with a 100% Fire Double Axe, drop that 80% Fire Resist down to 45%, then Double Strike the hell out of it while Onslaught is up. The 50-70% Hit Life Drain that Whammies can get with Curse Weapon (70% if in Vamp Form) can probably out heal it's damage output.
Could also use a Wolf Spider or Arctic Ogre Lord to tank it, due to them having 100% Poison Resist and that creature does 100% Poison Damage.