What's overpowered about it? It's just a feat from the Complete Adventurer with the requirements stripped down. The fact that it will only ever use that ability on the one person it was designed to strike against kind of mutes the lethality of it, anyway.

I don't think this is something a DM would send at somebody to actually kill them, but it's a great story hook. What would a character do, knowing that he is slowly dying a little more each day?