Hmmm... I have to say that  there does not seem to be a lot that one can do with shadows,them being intabgible manifestations of a lack of light, but if you can reshape them, I suppose that might have some bearing on, I dunno, freaking people out if they're around the corner. Manipulating it wouldn't really do much, that I can think of. Maybe I'm just thinking too small. But I can see useful implications for traveling through shadows if the character can then turn shadows into doorways. They could then potentially cut someone, if they're too big to fit or if the fall on the edge of the shadow but are pulled through. And there'd be other aspects to think of like what happens to them when they're going through the dark, and how they know where they're going. Actually manipulating shadow just sort of strikes me as hard and kinda pointless unless one happens to be in the circus and likes putting on shadow plays.

I do have a suggestion for Slice and Tempus, though the latter would likely only work if it's a turn-based, tabletop thing. Which I'm assuming it is based on what's been said so far. But rather than letting the character go back in time as many times as he can withstand, even if it is only for a few seconds, why not allow them to mess with time without being able to go back themselves? I think it's the spacetime theory? But if they could flip the order of two actions around in one or two turns, only two actions mind, and only things within a certain timeframe, that might give them a little more leeway, without either taking away the point of timetravelling(a few seconds really isn't a long time at all) or giving them too much power. This would need more thinking about, certainly, for instance, would causal actions be switchable, like throwing a glass and it breaking, or hitting someone with a sword and them falling over? And how much leeway would they have in defining a causal action if they aren't switchable? Someone drinking wine after it's been poisoned vs before it's been poisoned, for instance.... If that's something you wouldn't mind allowing, then you could say that the character would have to be able to guess or know which actions would achieve the goal they want(so they might not succeed in whatever they're trying to accomplish even if the actions do switch) and both actions would have to be within that limited timeframe(ie if someone had poisoned the wine days before it was drunk, they would have to find another solution, if they can). 

As for Slice, I see the point of an adaptable arm, and the unfair point of having to know how to make a plasma blast. But I think the whole listing what's in the arm is a good idea. And might do with another list of potential possibilities so that the player and the character both know what the arm is basically capable of before starting, and what you'd be willing to allow or not allow. But a true weakness should be set in place concerning maybe, power limits(do the batteries need charging?) or weight(the more equipment the arm has, the heavier it will be, the more lopsided the character's balance...)