[quote=@Nemaisare]
Would it be possible to reuse the old rolls for the previous actions and simply have the other players quickly put them to another action?[/quote]
You could do, but this could then lead to problems of over overlapping results. Going back to the guards example, the three guards enter ally #1 shoots guard #1, ally #2 sword swipes the guard #2, Tempus shoots at and misses guard #3. Tempus resets and shoots guard #2 instead, ally #1 shoots guard #1 and ally #2 is now charging down the corridor to engage with the already dead guard #2. This would leave guard #3 with a perfect opportunity to gun down ally #2 as they stand in the middle of the now corpse-filled corridor. Trying to switch the melee attack to guard #3 would cause problems as the difficulty of the attack would be different and ally #2 may not have succeeded with the same result.

The only way for the player not to find themselves at a disadvantage due to Tempus's interference would be to allow ally #2 to change the action they took in response to the interference, leading to a different outcome. While this would be fine as a one-off instance, with Tempus's powers firing off during every engagement the game would change from a plot-driven narrative to a long sequence of replays as each session ran ove4r the same engagement over-and-over until Tempus came out on top (or the other players get bored and head over to McD's instead.)

[quote=@Nemaisare]
I actually did mean causal, not casual.
[/quote]
My mistake there, too used to dealing with typos on these boards. :)

The problem with determining the causal links in a chain of events is how far back do you take the chain and how do you account for changes in the chain which may have been caused by the smallest of actions, Butterfly Effect and all that. Different characters may also choose to do something other than what they had the first time round after Tempus reset, plus the players may choose to make use of their own foreknowledge to alter events, even though their character's wouldn't be aware of the change in outcome (cheating bastards that they are.) 

[quote=@Nemaisare]
Either way, I can see why this could have the same problem with the whole having to redo the turns for the sequence things all over again that being able to go farther back in time would have. Though a limit like, you can only do this once every twenty minutes in game, might work to make that happen less?
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THe Star Wars roleplay system handles this in a good way by having Signature Abilities for high-level characters. These require the players to use Fate points to trigger the effect, require them to pass a skill check AND can only be used once per session. With these sorts of limits I'd be willing to allow Tempus a one-time free pass on time travel, with the warning that he may not even succeed if the skill test fails.

The physical travel through time rule would still apply though, so if he's almost dying after a particularly bad combat then he still wouldn't be allowed a miraculous cure by jumping back, although if there was a healer/medic in the party he may be able to get aid which wouldn't otherwise be available.

[quote=@Nemaisare]
Oh, there's a plasma core. I have no idea what that means other than really hot fourth state of matter, so I'll just think alternative power source and be happy with that. :P I wasn't thinking too much have every component be singularly capable of one thing, just that along with the list of every component, the player might offer you a second list of basic arm functions and ideas they have so that they aren't always stuck having to quickly think up something, have some practise at thinking up combinations, and know what you're willing to let sneak past if it's not exactly scientific. Then you both have some idea of what the other thinks is acceptable and willing to compromise about.
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I'll be using the Treknology rule for explanations on how the arm works, which basically means if the explanation looks logical at first glance and is consistent with what has happened before then it can be done, even if it's scientifically unsound in the real world.

Slice is a previously developed character the player wants to bring into the adventure and he seems to know what her limits are already, her backstory has all kinds of details which sound semi-plausible (like the arm being built out of a metallic crystalline lattice material which can grow along the paths of electrical current. making it easily compatible with Slice's nervous system.) I've already asked him to provide me with a list of the components he has at her disposal and what kinds of effects these would be used for. Once I have the list I'll check it and may veto anything which would give an unfair advantage (like a flux capacitor.) 

[quote=@Nemaisare]
I still say that a cyborg arm is going to be heavier than a regular flesh and blood arm, that, or it would be more easily damaged, particularly if it has the same amount of working parts. If something heavy hit it, instead of bruising, it might jam one of those components and until it can be fixed or rejostled into place, that particular component would be capable of reconfiguring with the rest. And whether or not those components work together or singularly, the rule of the more there are, the heavier it'll be still applies. :)
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Crippling the arm will be treated the same as a normal arm, making it useless until repaired, the only difference being it would need a mechanic rather than a medic to o the healing. Since Slice's main role is to be a method of transportation for her arm, which is the basis for most of her abilities and attacks, I'm not going to set too high a limit on how easily it would get damaged, since it would be unfair to have her one ability taken out of action every time someone managed to hit it.