When using MC, I have seen people on this boards turning off "optional" powers like Impervious and Mastermind. But since the MC'd figure becomes on the opponent side again right after the action they take, and since you have to take the action immediatly, wouldn't the person owning the figure be able to turn the power back on? Or does this require being able to use the fig during an action or something of that sort?

Optional powers, once turned off, stay off for the rest of the current turn. So even though player 1 may have regained control of his Superman that player 2 just MC'd, if player 2 turned off Superman's Impervious, it would not be active again until the end of player 2's turn.

I recall seeing a recent posting that advised that under the new rules damage-reducing powers cannot be optionally turned off. I'm looking for a judge who can answer this, or someone that can point me to the official document where this is spelled out. Thanks.

You can turn off all optional powers (this includes Impervious). Toughness and Invulnerability are not optional. Unless the "optional" indicator is removed from Impervious the Icons PAC (and I have heard nothing to indicate that it will be changed), then you can still turn off Impervious.

And in case you are wondering, the reason Impervious is optional harkens back to the original wording of the Power, when it performed like a combination of Super Senses and Invulnerability. On a roll of 5 or 6, the attack would actually miss, not reduce to 0. The Power description was changed to the current wording in Indy, I believe, and for whatever reason the "optional" descriptor was maintained.

When turning off IMP in particular does it do full damage or it still gets reduced by 2, only with no roll.

Full damage is done. When *any* Power is turned off, it is basically the same as Outwitting the Power.