Master Speed is named Force Power, thus falls under the stacking rules. The generic "move faster" and "reroll" are not, thus are allowed to stack.

Even on effects that don't replace attacks, named Force Powers do not stack unless it explicitly says they do, so Master Speed doesn't stack with itself.

You could, for example, Lightsaber Deflect two different attacks in the same turn, though.



Minor related technical question: could you use Lightsaber Deflect twice on the same attack? Usually a moot point since you could just re-roll it if you miss anyway. I'm just curious if that would count as trying to 'stack' Lightsaber Deflect. This would only come into play in the strange situation where you manage to give MotF2 and LS Defense to a character with Force Ascetic, since they wouldn't be able to reroll.

That would be stacking.

Yup, this would follow the Lightsaber Riposte ruling.

This should be covered under stacking in the rulebook. The rule is pretty much, you can only benefit from an ability once per instance of use, unless it says otherwise.

The stacking rule:

stacking: In general, the effects produced by Force powers, special abilities, commander effects, and cover stack (are cumulative) with each other. For example, Tarfful grants followers within 6 squares a +4 bonus to Attack against adjacent enemies, and a Wookiee Berserker has Momentum, which grants an additional +4 bonus to Attack and +10 bonus to Damage against adjacent enemies if he has moved at least 1 square. Thus, a Wookiee Berserker within 6 squares of Tarfful would get a total bonus of +8 to Attack (as well as the bonus to Damage) if he has moved at least 1 square and attacks an adjacent enemy.
Unless otherwise specified, no effect produced by a Force power, special ability, commander effect, or cover stacks with itself. For example, a Clone Trooper Commander can give nearby Trooper followers a +3 bonus to Attack, but two Clone Trooper Commanders together can’t give a Trooper follower a +6 bonus.

The key is in bold. However, I will repeat it in case bold doesn't appear. Unless otherwise specified.

Here is master of the force again in the rulebook:

Master of the Force [#]: (Force) A character with this Force power may spend Force points up to the stated number of times in a single turn. This character can also spend Force points more than once to take the same action (such as moving an additional 2 squares or rerolling an attack).

Again, in bold is the key section, again re-posting it: This character can also spend Force points more than once to take the same action. The part in () denotes examples of, not the whole of (as it seems to be interpreted as), what is exempt from the rule.

One last point. The stacking rule specifically states the following: "Unless otherwise specified, no effect produced by a Force power, special ability, commander effect, or cover stacks with itself." The rule states EFFECT by a force power, SA, CE, or cover stacks. Preventing damage through abilities like parry and evade and ls defense more than once a turn would seem to be the same effect caused by one ability. However, Parry and evade state "whenever", denoting they can be used more than once, LS defense, however, does not have that distinction. It is only able to be used through MotF and only because it states they can "spend Force points more than once to take the same action" in one turn.

As such, the same should apply to abilities like sith rage OR not apply to abilities like force alter it is the same ability for the same effect. (which it currently does)

But what I am asking is why can you use it twice but only gain +10 from it. I know you can use it twice if it gets absorbed, however, if it can be used twice that means you can be effected by it twice, meaning +20. There is no rule that prevents gaining more than one stat boost, only more than one from the same ability unless otherwise specified. If you can use the power twice and it is because MotF allows you to use the effect twice, it should grant +20 when used twice. Even more so, Master speed does not effect movement for the entire turn. You can use it before or after a mobile attack, meaning it is broken into two separate movements. By the logic you used for sith rage, you could move 12, attack, then mobile 6 with Master Speed.

Can you show me where that distinction is made?

Flip it around. Saying an ability does not stack is not the same as saying it can't be used twice.



The 2nd instance just has no effect.

You can use Rage twice because it does not replace attacks/turn, and does not state "once per turn..." But the bonus will not stack because it is the same named ability, and it doesn't state that the bonus stacks in the ability definition.

The only reason I can think of where you would ever use it more than once is if the first instance got cancelled.

The decision about whether to use Lightsaber Riposte and Lightsaber Block must be made immediately, but then they are resolved in whatever order the player chooses (simultaneous effects). You can't use Riposte or Block twice on the same attack due to stacking rules.

LoboSteele explains the speed issue nicely here - http://www.swmgamers.com/forums/viewtopic.php?f=53&t=10401&p=120807