Angel of the Ailing
You are a former ass kicking marine! Back in your day, you raided hell and destroyed the cyberdemon, and you have the scars to prove it. On the verge of retirement, you gain word that your old pal cybie is back and all the new recruits have failed to take him down. Return and show these fresh whelps how it's done!
You start as a level 20 marine with an inventory full of BFG, chaingun, large med kits, etc. Enemies grant no exp, you already have plenty of that. However, you haven't been keeping in shape and you're not used to this kind of mental and physical exertion. As a result, every dungeon level you pass causes you to level DOWN, losing one of your much loved traits. If that wasn't enough, the strain on your aching back prevents you carrying as many items, and your inventory spaces decrease by 1 ever level passed. This is surely a one way trip...