Sounds like the WFRP novel Drackefel (sp) or Venom.
I would make it a template, where powers kick in at levels. Low levels; good AC, later; increases the characters speed, later still; vampire hit recovery (for damage done to foe, player is given a few points back). The problem is you have to watch it so you do not produce an over-powerful character, so now balance it out with drawbacks at some point. Example of this, berserker rage to get the vampire hit point recovery, player has to save or go into rage.
1) Leather armor with AC as scale mail
2) Increase players reaction time by +1
3) AC increase +2
4) Reaction time +2 & hit point recovery (3pts for foe killed)
5) AC increase +4 & Non-Class special ability (burning hands/night vision)
6) Reaction time +4 & hit point recovery (5pts for foe killed) & Rage
Sleeping in armor has drawbacks that could apply to this situation. No, I don't remember any of them right now.
Something like penalties to skill checks, not fully rested, you're grumpy, etc.
This is great! Thanks! I'm not really sure how to do the whole 'grafts onto your flesh vs. removing it + some of your skin with it' thing, do you have any suggestions?
Do the slug - first a bit of little slime here and there, this numbs the flesh, later, feelers start to attach themselves. Later still, it is a STR test to remove the armor, roll x times for number of parts, each time the player fails looses 2 point of CON, 1 point for doing it. If he goes to zero, he is knocked out and the armor starts to climb back on him. If, he does to -5 CON he dies!!!!
I say CON because this is the body of the player and hit points just doe not proved the effect, hitting at a player's STATS effects them differently and takes them out of a comfort zone but HP could be used, damage could equal HD of the template, say it was at 6 level that would be 6d10 for each part.
this is litteraly EXACTLY what i was looking for! You're amazing!