What are reasonable limitations to this character's reality warping powers in Gurps?

[MonkeySage]

This character, Dario, is the son of a witch and a demon in a superhero game.
Dario's primary powers are supersonic flight (from a pair of fiery wings he can spawn from his back) and limited reality warping.

Dario can, using his RW:
Heal a single injury at a time.
Keep himself from dying.
Boost his physical strength to superhuman levels.
Pass through walls.
Alternatively, he can simply make a door appear in the wall.
Create small objects.
Cause himself to vanish from sight.
A few other tricks that I haven't thought off.

He cannot:
Turn back time.
Bring back the dead.
Heal more than one injury at a time.

His RW is limited to what he can touch, he can only perform one RW at a time, and he can't RW if he loses consciousness.

Since this is a superhero game, the DM has said that rule of fun is largely in effect.
However, I don't want this character to be OP, which is hard to do while he has this ability. So I wanted to come up with some reasonable limitations to this ability of his.

[Keltest]

Make it take a great deal of concentration to use effectively. If he is sitting there and meditating, he can create a video game console or something, but if someone is chasing him or something, he could struggle to make a simple hammer.

[Maglubiyet]

Some Limitation ideas:

• Limited Uses -- only a certain number of times per day
• Costs Fatigue -- drains FP every time you use it
• Nuisance Effect -- each RW use causes you to look more demonic (larger horns, skin turns redder, eyes get more reptilian/cat-like, smell of brimstone, etc.) causing an additional -1 reaction penalty (approaching Hideous or Monstrous Appearance, Disturbing Voice) until you have a chance to rest and recover
• Accessibility -- does not work on "holy ground"

[mikeejimbo]

How is the Reality Warping built? If it's built as Modular Abilities, you're already fairly limited by the point-cost of your pool.

If you work with your DM, you could get the MA built as something similar to a "Grimoire" in that you're severly limited to the selection of abilities you can use (a list you and the DM work out ahead of time), but you could get a fairly substantial point cost break for that.

Otherwise, the suggestions Keltest and Maglubiyet posted are good. You could build Keltest's suggestion as Weakened Without Preparation, and define the "Preparation" as time spent Concentrating. "Requires (Attribute) Roll" could also be good, and you could define the weakening as a penalty to the roll. Take a page from the Warp (hah) Advantage: -10 for instantaneous use, and maybe each second you take a Concentrate Manuever first removes 1 point of penalty from it?

[Mr Beer]

I would like to see the build, it may be self-limiting. Alternatively, if you spent a ton of points on it and everyone else gets the same budget, I don't see a problem.