Whoah. That is scary; I was tempted to do a solo campaign where the player was struggling to find a way to exorcise a demon from their body- but I figured nobody would want to play it since, A. D&D is a social game, and solo-adventures are more fitted for a Neverwinter Nights module than a Human DMed game, and B. The story might ineivitably lead to a tragedy, but with multiple outcomes.

Seriously, if the player was in danger, the demon would manifest its powers (at the cost of your strength against the demon's spirit, so being near-death often would shorten the campaign considerably.), and the concept was that the demon was the emboidement of wrath; primarily fire-based abilities.

Actually, The whole concept of my earlier thread somewhere about Adamantine being impossible to forge was based on tinkering around with fire damage against metals. Essentially, the demon's ability was that when you were near death, your skin becomes hot as lava, hot enough to melt any armor your wearing in a round or two. (another reason to avoid letting the demon do all the work. ;-)) and anyone grappling you is in deep trouble. It didn't prevent damage (except fire), but weapons would take severe damage for touching you, and you gained a pretty powerful unarmed attack by proxy.

Spooky. Of course, I love the idea- I just wish I put it out there before you. ;-) (Mine was an aquired template, though, not a class. :-P)