Because all special powers are optional, if I use Nightshades special power to put up smokecloud, and for some reason would not want it there, could I option off the special power so she can no longer use smokecloud and then the 4 squares of hindering would be removed?

I believe not., no.

No. The markers only vanish if the power is lost or countered. Cancelling a power does not mean it is lost or countered, only that it is not being used. The Smoke Cloud would remain.

Correct.

This is like the trick people have tried in the past with MCing a guy to cancel his Outwit. It just doesn't work.

To reiterate - if you outwit barrier or smoke cloud the tokens come off the field right?

If you mind controlled Nightshade to place her smoke cloud underneath her and her teammates would it cause them damage? It seems like it wouldn't since as of that turn it would be under friendly not opposing characters - but it was originally placed by an "unfriendly" character, yeah? I'm pretty sure the answer is that it won't cause damage - but it came up in a game the other day, and thought I'd get some verification.

"Attack - From the Land of Nightshades: Nightshade can use Smoke Cloud. If an opposing character ends its turn occupying a square containing a hindering terrain marker placed by Nightshade, that character is dealt 2 damage."

Yes

I would say that if she has Smoke out there, at the end of any turn any figure on that team in the smoke takes damage if it is opposing at that point.

I may have read your message wrong, but if I didn't...

If Nightshade was mind controlled to use smoke cloud, after the action resolves she becomes friendly to your force again, and would eliminate the "opposing character" problem. Even if that wasn't the case, her power reads any character ending their turn in the Smoke Cloud takes damage. Since your opponent is controlling her, you don't begin to give any of your characters an action till the beginning of your turn. And by then Smoke Cloud disappears.

She's always opposing to someone.

It is just a two player game, me versus you.

On your turn, you MC her.

You put Smoke out. One square is under my Moloid. One is under your Gotham Detective.

The action ends, returning her to my force.

Your turn ends. Your Gotham City Detective is a character opposing to Nightshade. He's ending his turn in a square of her smoke. He is dealt 2 damage even though she was friendly at the time you put it up.

My turn begins. The Smoke stays up because it doesn't come down until the beginning of your turn.

My turn ends. My Moloid is friendly to Nightshade. He's ending his turn in her smoke, but as he is friendly, no damage is dealt to him.

The smoke now comes down and your turn begins.