I assume that you can turn off Special Powers any time during your turn, and that they stay off until your next turn. For example, Emperor Joker can use his Embiggen SP to hit a figure two spaces away, then cancel it to become normal-sized until the next turn.

But what about Special Powers that have multiple effects? The simplest example is Gambit's Speed SP that grants him Running Shot, Leap/Climb, and Stealth. Can Gambit turn off Stealth but still have access to Running Shot and/or Leap/Climb? Or does he have to cancel his entire SP (losing all three powers) in order to not be stealthed?

This came up in a game and the ruling was that since the power says he "can use" all three powers, he can cancel them individually.

You may turn off special Powers anytime you could turn off any of your "normal" powers. That is, not in the middle of another action.
Any special power that lets you use X,Y,and Z powers, you can turn off any of them without effecting the others.
Any powers that are turned off come back at the end of the current turn (not the end of the next turn).

Not true.

You turn off the SP, you turn everything off.

There's no, "oh, I want to keep RS/LC, but let's get rid of stealth."

Nope.

I would think it would depend on the wording, also I dont think you could cancel out embiggen, it says he has the big symbol, not "he can use" he's a giant till it comes off his dial.

It's true that if you turn a SP that lets you use multiple powers, that it turns everything off.

However, all the SP's that let you use multiple powers, as far as I know, actually use the keyword of allowing you to use the special powers. Thus, you can choose if you wish to use each individual power or not without actually having to turn off the special power granting all of them.

It's very confusing, I know, since you're not actually cancelling the power like you used to have to do, but this seems to be the case now.

Esper is correct, the keyword to remember here is "use". If an SP allows a character to "use" a power(s) it is optional. Take the Batman TA and someone w/ Stealth on their dial. While the Batman TA lets you use Stealth it is not required to be canceled in order to be PC'd by a friendly fig. Where as, someone w/ Stealth naturally on the dial has to "turn off" Stealth in order to be PC'd. So I could RS w/ Gambits SP put him in hindering terrain and PC him if I miss my attack, then when you go to attack me I "use" my Stealth granted by my SP.

Hey, anyone know where it says all Special Powers are optional? I'm having a hard time convincing my judge about Embiggen.

you can turn off Embiggen.

It's not going to say "this power is optional" it will say "this figure can use...". It's the "use" part that allows the character to pick which power it is using.

Gambit for example, his SP states he can use L/C and Running Shot. Can he use them at the same time? No, because L/C is a Move Action and RS is a Power Action. So you choose which power to use.

Joker can stop being a giant if he is targeted from range to avoid getting hit which would last until the end of the turn.

Here ya go.

Another thing NBPerp stated about Special Powers (although I can't seem to find the thread):

Since SPs that grant multiple powers say that a figure "can use" a certain power, each of those powers is turned on or off on a case by case basis and not required to be off for the rest of your turn and until the end of the round.

For example: if you have a character like Nightwing who "can use" E/SD and CR, you can choose not to use E/SD to use Compel on him, but then turn it on if he's adjacent to an opposing figure you are using EE against and vice versa. It's not off until the end of the round if you choose not to use it at some point during the round.

It's on page 13 of the Legion rules book.

Just to help clarify some confusion that may have been caused by use of the word "optional":

If you have a special power that allows you to use powers, you can choose to use the power or not on an action by action basis.

For example, if you have a special power that allows you to use stealth, you can choose not to use it when you want your perplexers to perplex you and then choose use it when you take an action in order to prevent opposing pcers to see you.

So, if you have a special power that says you can use another power, use of the power is optional in that you can choose if you want to use it or not, allowing you to essentially turn it on and off during the same turn.

Now the confusion may come in with regards to powers that are (optional) according to the PAC. This differs from the PAC defined (optional) powers in that with these powers, (optional) just means you can cancel it. Once cancelled, the power is off until the end of the current turn.

All special powers are (optional) as well as many of them allow you to use other powers, so it can cause some confusion here.

So in a nutshell, special powers can allow you to use other powers. If they do, the powers your special power allow you to use can be turned on and off on an action by action basis. Note that the entire special power is still (optional), so if for some reason you wanted to cancel the special power, you could still do so.

Hope this helps! The new focus on the word use really changes things from how they were in the past, so it's very understandable for there to be confusion about it.

This is also why the Mandarin uses TK with Poor Teamwork in play.

Okay, there's a huge misconception here. Special powers that allow you to use a power do not get "turned off" or "turned on" on an action-by-action basis. Once you turn off a power for any reason, it's turned off for the rest of the turn. Special powers that allow you to use a power simply give the choice to use the power on an action-by-action basis. When the action comes up that the usable power might be used, then you say, "I'm using it" or "I'm not using it". To actually turn it off, you'd have to turn off the whole special power and it'd be off until the end of your turn.

Using the terms "turn on" and "turn off" to describe the optional nature of special powers and the powers they allow a character to use only causes further confusion. Please don't describe them in that manner. You're only creating another mess for someone else to clean up later.