One of the first I thought of is possibly the riskiest XD... but might also be really entertaining to see interactions between him and mister 'reset things to reality' there >3>
Keep in mind, these are just ideas, I have others, but these were the riskier ones XD I'm not 'pushing' to use one or the other, just fishing for opinions.
Chaotic Reality Manipulation - I know 'exactly' how ridiculous that sounds, but here, lemme make it sounds less rediculously OP ;3
The 'power' is obvious, Warping reality around him, an ability so broad and unrestrained that the limitations imposed on it speak more for the power's nuances than talking about what it 'can' do... granted, this kindof digs into concepts, and there'll likely be some other limits I don't think of at the moment XD
The first and biggest limit is 'chaos'... Conceptually, this implies things are never certain, something different can always happen. In short, He cannot, or rather it is hard, to do things that have an ensured unchangeable out-come... For the most part he can circumvent this temporarily, such as resolving himself to undo something later, or simply by knowing that someone who can 'fix' the problem he caused is soon to be involved, though the primary unchallengable portion of this rule is that he cannot 'kill' using his powers, he could perhaps use his power on 'himself' and the utilize something unrelated to do so, but death is by some concepts the antithesis of chaos, and thus he is not capable of 'causing' death using his powers... in-fact, attempting to do so tends to cause his powers to just not work and emit a deafening air-horn.
The second big limitation is that, seemingly at random [read, plot relevance], use of his powers will have a 'fair play' rule imposed on them, disallowing him from using them to such a degree that his target has 'no' chance to win, or survive, or to reach whatever goal he may have been disrupting. He can get around this 'sometimes' with ingenuity, such as creating a maze and changing it's layout mid-way to change the path to the goal, as 'changing' it suddenly is pretty chaotic, though he cannot use this to make it impossible to reach the goal.
A third limit, which is somewhat less of a limitation and more of just a quirk, He has to snap his fingers for any reality alterations beyond 'small' or 'simple'... for instance, he can conjure a drink from air with a thought or float around, but to warp a room in it's entirety he'd have to snap. This has the added effect of producing a loud echoing snap that can be heard anywhere within roughly 10 meters of what he changed, so it is heard farther depending on how large the change is... This isn't much of a 'limitation' but it means anyone who knows that he is a thing will know when he's nearby and doing something... If anyone realizes this, then they may also be able to restrict how much he can do by binding his hands.
A fourth limit states that his power cannot be 'unchallengeable', he can push back against other forms of manipulation that relate to something he can do, such as struggling for 'spacial control', or against something trying to fix his 'mess', but doing so requires his focus and makes it difficult to do anything else.
A range limitation could also be imposed, making sure he can only affect things in a certain range, though the effects remain while he is far away, he cannot fix, maintain, or defend his changes without being close enough.
I know, there's always a shape shifter ;3 heheh, though I have a couple of different versions for this.
The first one might be considered similar to the old 'martian man-hunter' theme, in that someone's power isn't so much 'shapeshifting' in itself, as being turned into a creature who 'can' shape-shift, and may have some other supplementary advantages and weaknesses, such as differing nutritional needs, a base biology that would be weak to something new, or of course a monstrous appearance that would frighten normal people. I actually have a 'lot' of fun experimenting the possibile instinctual and personality changes that come with alternate species, like insectoid creatures for instance >3>
While the second is simply using the stipulation from the first, which i'll describe here, without the 'change in base species' bit.
In both cases the shape-shifting idea I like to work with depends on a biological understanding of the change that one wants to make. If someone wants to make claws for instance, they have to have an understanding of how claws 'work' biologically, what makes them what they are, how to create their durability, their sharpness... otherwise they'd likely make something that 'looks' like claws, but has no edge XD
This version also comes with a built in weakness, since it's not 'I will it so I change' kind of shapeshifting, and instead deals with modifying biology directly, 'mistakes' can range from annoying to potentially fatal, from some uncomfortable accidental material replacing some skin, to accidentally morphing a bone at the wrong angle, or tweaking the wrong organ [imagine the mistake of trying to mimick someone who's heart is on the opposite side of the body, but only not knowing 'that' quirk.]
This form of shape-shifting is 'technically' without limit, but can only progress so far as one's understanding of things can reach. It also depends on the amount of material they have to work with, preventing them from turning into some big dragon thing that'll just stomp everything into dust... at least, without some hugely dense pockets of material to work with. [we're talking tons though XD ]
This also has other 'realistic' effects to it, such as while he'd have the option to morph parts of himself to be more 'dense', in order to store greater ammounts of material, that also makes him heavier, and thus some surfaces become less and less viable to move on stably without falling through XD The added mass also has to come from somewhere, which along with the 'cost' of greater shape changes, usually comes with a 'huge' appetite. XD
This is a power with the utmost potential, but requires learning, time, and experimentation to progress farther along in certain areas... for instance, changes in color, minor size changes, or minor density alteration would be easy peasy, imitating a human accurately might be more rough in scope, but ultimately easy to practice, things that Science already knows through and through, since there's ample material on the matter to read about. However, while he 'has' the potential to morph the necessary qualities to, say, 'eat metal' that can be re-used to form some titanium claws or metal skin armor, he 'first' has to experiment and find the right way to make this 'work', or risk causing horrible side-effects from bits of metal being inside of him without the proper methods of digestion prepared.
Of course, I usually include an 'emergency reset' facet to the power that can prevent him from killing himself, but usually results in a lot of desperate use of his power to 'force' things back to his base natural state in order to ensure survival and remove any foreign materials, typically resulting in some exhausted and vulnerable state.
This one's considerably simpler than the other two, but is considerably broader than 'earth' or 'nature' powers usually are XD The implication being an incarnation of the earth itself, though that does 'not' need to be extra powerful, it's more so for the theme >3>
It usually reffers to their body being made to emulate the state of the planet, Stone, naturey bits, magma blood, some water, weather, or gravity effects, things like that XD It can come across as a combination of other powers, though the actual extent of each one in comparison is usually lower compared to specialized powers when it goes beyond stone or nature themed abilities.