In my fantasy WIP, the MC is just a regular guy (no chosen one or hidden parentage or prophecy involved with him). In the back-story of the world, special abilities and magic was once common. Then the big bad caused a war with Earth and Heaven that nearly destroyed both worlds and since then magic has been greatly reduced to the clergy and some devoted fighters willing to push their bodies to the absolute limit. The MC accidentally stumbles on some kind of macguffin that gives him the same kind of power the Big Bad had back then. And it's enough for the clergy and the government to be interested in him. The problem is I'm not sure what kind of powers to give him that would allow that to be the case. I originally thought of seeing through demon disguises but the clergy would already have that (or some form of it). Then I thought that maybe he could use both the magic based on Earth and the magic used by the Heavens. But then I thought it would make him too powerful and it sounded a bit like Avatar: The Last Airbender or something. So I'm currently stuck. Any suggestions?
Hmm... You'd have to share more about the kind of world it is. Give us details! Also, a great way to make the character more valuable is to make not just the macguffin, but he himself a threat. Anyone can use a powerful object, but using it a unqiue way for maximum damage is what really makes them important.
Well it's a world based on Eastern mythology so the magic is actually "ki/chi" similar to the animes like Naruto, Dragonball, Yu Yu Hakusho, etc...where people push their bodies to the absolute limit and beyond to be able to do the amazing things they do. The MC is just a village kid (that's one cliche I actually like), who just wants to get out and see the world. Problem is he and his people are refugees from another country and so the government doesn't allow him or anyone one foreign to just wander around without the proper paperwork and every time he tries, he always fails the tests because of some technicality. The government and clergy are in an uneasy alliance because there have been rumors that the Big Bad has returned somehow so the government has sent two agents to investigate the claims and the clergy has sent an acolyte as her final test to fully become a member. The MC runs into them when demons force them to split up and does something to make both the agents and the acolyte see the potential he has to further their goals (both professional and personal). I just don't know what the MC could do though. Is that enough detail?
Being super powerful could work, because you could make your character terrible at using it. Maybe give an advantage to the bad guys, simply because the MC causes such destruction with his omnipotent powers? But NeonFraction is right, we need to know a little more about your world. Are we talking elemental magic, dark/light magic, magic which uses summoning and bracelets and chanting and whatnot? Tell us more and I'm sure we'll be able to provide more in-depth answers. Edit: now that we know more about your world, how about you make him a little bit like Dr Manhattan from Watchmen? If you haven't seen or read it, I suggest you read it first (but both mediums are excellent). He can bend matter and is basically a god to the humans. Would this fit into your world? It could also work because it could fit into the whole heaven and earth kinda thing.
Astral projection sounds like a useful power for someone who can't travel but wants to. And his body could be vulnerable when he's out of it so he has to hide it well when he projects. AP is a much older myth than Avatar (the movie) and I think with a little research (see Carlos Castaneda's stuff) you could make it unique enough for your story.
I'm not really sure how your demons are going to work, but perhaps you could give him some means of permanently killing them or something like that. If they are those kind of demons.
