"This? Ohoho," Minacious moaned, "Fire resistance spell, mmhh, means I can set the body I posses on fire and, aah, emerge unharmed! Consider it a demonstration of that magic you begged to see."
"So, wait, you can set yourself on fire and it doesnt hurt?" Grim asked.
"No," He snorted, "This hurts like Hell. Trust me, I would know how Hell hurts."
"You're hurting yourself on purpose?" Grim said, "Hang on, no, you're hurting my body on purpose!"
"Your body's magic was capable of this spell, so I figure it's worth keeping around, at least for a while until I get bored. You can have whatever's left then. Are there any electrical lines nearby? Where's the nearest railway?"