He's just asking the dark powers to take notice of his character, and I made him fail the first powers check, though what he did entails around 3-4 weighted checks according to the PHB.
I'd prefer to curse him though and let him lead his character to his own demise. I haven't had much experience in the crafting of curses or failed power checks though, I started his character down the path of the ringleader to keep the game moving, but any suggestions on curses or alternate path this guy should take?
I'd go Path of the Brute: It fits the actions he's been doing and plus, his rogue may not like becoming a huge hulking monster...
All the following are on basis that you don't run an evil or wanna-be-evil campaign.
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First of all, you have to make sure (by alignment test?Future actions?) what is your player's, not character's explanation of the event. If it is inadequate, I will have to agree with Quentin for his point. Over my series of Rloft campaigns or "quick expeditions" I have encountered many cases of power mad players, who, having misread the Rloft Campaign Book think in a way like "Ooooww, these Dark Powers are SOOOO kewl, so because I'm a great player I can outsmart them and stop before becoming npc" etc. You can get the point.
THIS KIND OF BEHAVIOUR IS W-R-O-N-G PEOPLE !!!!!
Power checks is a very important part of the Rloft IMO, changing the course of an entire campaign if taken lightly. .
At first I advise you to follow Jethro's idea. Give your players an embarrasing or mostly useless power/curse (e.g.: his/her ears glow when near gold/undead/danger) BUT keep a sharp eye out for signs of disappointment. If so, SMITE the player mercilessly. What I do is take back the silly effect ("the Lord giveth but the Lord took back
) and, like Quentin said, find out the most annoying and disadvantaging "gifts" the powers can give the player at the moment.As for the gifts themselves IMO you have to plan beforehand a series of neat candies for each character
. At least that's what I do. I sit down at -inbetween games- time and create a list (e.g.: a hunchback for the rogue= +something at tumble etc/-something hide and disguise or a set of fangs for the -weak at combat- party speaker... ;) ). That's the usual stuff, for not pretended "falls from grace". In case of types like your rogue the answer is swift and painfull. I fail them automatically the first two or three powers checks (even if it means cheating the dice, I mean, the guy burned a friggin Ezra church!!!) and get them a nightmare trip. You shouldn't so much depend on paths, but if you want to, there are many submissions of paths over the net, I just don't remember where right now. (I'll get back to you on that). Just hurt him, any way you can. IMO, it's much more important than being an @ss to your players. ANYTHING GOES, because it's not "the evil character", it's "the power hungry player". Use whatever you want, even the worse curses.
I hope this all helped, but remember......
....It's just a game!
Failing the first stage could give him a bonus to fire saves, but he'll always feel uncomfortably warm, even in the middle of winter.
As the condition progresses, perhaps he becomes immune to being burned, but still can _feel_ the sensations of being burned. Not a desireable thing if you happen to be torched by a mob. In addition, water or ice attacks would cause extra damage.
At the latest stages, I might give the player an effect similar to the old flaming fist spell (I forget the actual name, but it wreathed the casters hands in fire and would cause whatever he touched to burn.), but be unable to turn it off.
At the final stage, his body would be completely engulfed in flames that he could feel burning him, but never consuming his flesh. A pyre elemental in all respects, save that a living man would be at its heart.
Just a suggestion.
Also, a huge
to Deadbreaker for stitching together this track out of thin air (or maybe mist... 
)!Ever felt like you were surrounded by zombies?