Here's a real quick concept writeup. This is still very rough, just thrown together off the top of my head. Anything herein can and probably will change, so don't get too comfortable. [:p]
There's a lot of my love for Silent Hill showing here so far - bear with me if it seems derivative, it won't be by the time I'm done. And here we go...
Under the shadow of our reality, there is another. In this place, spirit is as potent as flesh, and your thoughts and feelings just might have thoughts and feelings of their own...
Once in a while an individual may stumble across this place and become trapped. Some wander lost for days or weeks before succumbing to starvation, dehydration, insanity, the local wildlife or each other. But some change, or are changed.
Those who are ruled by darker, baser emotions ? anger, lust, greed - will find those emotions growing far stronger and developing their own twisted, base sentience. In time this parasitic presence will grow, asserting itself and gaining control of their very flesh. The presence changes the victim?s body for its own needs, growing and spreading like a great, malign tumour. In time the remnants of the original soul is crushed, and its dark desires gain complete control, warped and mutated far from the original human flesh.
Urge slave ? while the individual still retains some control and sanity, the fledgling parasite has only limited control over the body. It is slow and stupid, clumsily trying to fulfil its horrible desires, staggering in pursuit of its victims, moaning, drooling and twitching. It does however possess a staggering degree of strength, and an instinctive cunning.
For all intents and purposes urge slaves are bog-standard zombies, except they?re not dead and are in better physical shape. They walk slowly, limping, jerking, twitching, moaning and mumbling as they go. The head lolls and flops around loosely, the mouth hangs open. They don?t blink. The longer they are in this state ? and the more horrible acts they commit ? the nastier they will appear. Clothes will tear, they will accumulate injuries, become splattered in filth and blood (blood, you hope :p). These guys are closer to Silent Hill nurses or System Shock II hybrids than Resident Evil zombies. They are zombie-like, but there?s a degree of intelligence and emotion motivating them, not just an empty stomach. In game terms they?re primarily an early challenge, helping set the scene and atmosphere, but they?ll be present throughout the game as a bullet sponge if nothing else.
Urge beast - when the urge mind begins to change the flesh of the victim, they become an urge beast. The urge beast in simplest terms is part human, part massive twisted nightmare beast. The urge-controlled flesh varies greatly by individual, but typically it is much larger and stronger than the urge slave, equipped with vicious teeth, claws, spines, quills and whatever else takes it?s fancy. Extra limbs and organs are common, and the human flesh is pushed aside to make room. Typically it takes the appearance of a horrible, evil Siamese twin of sorts, a blend of the original human and the final urge (see below), the human flesh twisted and weak, the urge flesh rapidly gaining control.
The urge beast is closer in concept to William Birkin of RE II than anything else. It?s obviously two minds struggling to control one body, with the urge winning the battle. Its mutations don?t need to be logical or sensible, although it will most likely take the form of a massively swollen quadrant of torso, one or two limbs hypertrophied, part of the face and head twisted around for it?s own needs. Maybe some extra eyes, mouths, etc. Their appearance will most likely stick to the urges and emotions that created them in the first place. These guys are the mid-game surprise. Just when you thought you had your head around the mumbling zombies, they get bigger, stronger, faster and pointier. It?s just not a survival horror game without the mutating enemy cutscene.
The final stage is reached when the urge takes complete control, becoming a fully fledged ? and fully fleshed - urge. This creature has no basis in our reality, and pays no heed to the physical strictures of our world. It exists only to fulfil the base emotions and desires that spawned it. It is inhumanly strong and fast, and is driven by hungers we are incapable of understanding.
The urge can take whatever form it likes or needs to do its nasty thang. It will probably have some remnants of the original human, even if only part of a face or an eye. This is of course your endgame tough bad guy, maybe even a sub-boss. Of course the concept outlined here would work for a main boss, spawned from a major character perhaps.
I've gotta say Bunny "this sounds very interesting!"
I can't wait to see what spawns from this vile peice of text. =)