I am going to be running a game in a few weeks and I am currently helping my players with character creation. One of my players has a pretty unusual character concept, and although I really like it, I am having trouble coming up with a satisfying way to design the catch for Inhuman Recovery power he wants to take. Let me give you a little bit of background on the character concept so you can offer suggestions.

His character comes from an old money family with lots of old political ties (think more Bush than Kennedy). He has been in big business since graduating from college, failing upwards as he runs each company into the ground and gets hired on to the next company for more money and a better title, trying to capture some elusive measure of success. Once he realized that he had risen as far as he could go and that he was now essentially radioactive, he started jet setting around the US to posh locations and high dollar hotels, trying to network and carve out something like his former life. He degenerated into drug use and eventually stumbled across a man convulsing in a hotel bathroom, apparently overdosing from something. Next to him was an intricately decorated ceramic jar with a dark liquid inside. For some inscrutable reason, his character decides to try the liquid, and immediately he gets an amazing rush; he feels younger, stronger and more alive than ever. He gets into a fight and realizes he could quickly become used to feeling like this, and becomes a thrill seeker, looking for a reason to use the mysterious liquid as well as looking for answers about where it comes from.

The liquid is actually created by a powerful magic user who has focused all of his magical power in reinforcing his existence and achieving immortality by never aging or changing in any fashion. The person is very powerful but isn't much of a force in the world due to the desire to only amass and use power to stay static and defy death. The jar is a part of the ritual, and the liquid is actually part of the person's essence that is pooling and distilling to then replenish him. By drinking the liquid, my player's character is essentially gaining a measure of his power, but it comes at a cost, as the character is slowly becoming more and more like the person whose essence he is imbibing, and he is having to resist having his thoughts and desires being taken over by this much more powerful entity.

In game terms, the character is an Emissary of Power, albeit in an unusual sense. My player has elected to take Inhuman Recovery as one of his powers, which makes sense to me. The catch as he sees it, is that as he heals damage, the entity gets a stronger mental hold on him and he has to shake off the influence. The problem is how to actually simulate this idea. I proposed allowing him to "heal" the physical consequence by trading it for a mental consequence of equal value. My player didn't think that was much a boon, but I worry that if I allow him to trade it for a lower level mental consequence, it might not be much of a catch. Alternatively he proposed that if the attacker used their "favorite" weapon, spell, or whatever, that it might bypass his ability to heal. I actually think that is too weak, and wouldn't make his power actually be much good to him, and he would quickly be dissatisfied as most enemies would use the their favorite weapon as their default and he would never benefit from the increased healing.

Any suggestions you can recommend are greatly appreciated!