Can a character with stealth in hindering use powers like perplex, and probability control on itself? Do they have to cancel their stealth? If so when does stealth come back?

They have to cancel Stealth. All cancelled powers return at the end of the current turn, so the only real drawback to cancelling Stealth is that your opponent can affect you with Probability Control.

Do you have to decide to cancel stealth before making an attack roll with that char?

yes you do have to cancel it before you attack.

Hey since this thread is a question about stealth, I figure I'll post one so as not to start another thread that may not be needed. It was drawn to my attention as to the wording of the Batman ally team ability and the actual power of stealth that stealth can work even if the figure that has it is not in hindering terrain. The description of the power reads this way on the Danger Room PAC and on the Icons PAC not to mention in tell the Batman ally TA:

STEALTH (OPTIONAL): Any line of fire drawn to this character that crosses hindering terrain, including a square of hindering terrain occupied by this character, is treated as though it crosses blocking terrain.

The question is that the way that last half of the description reads to me sounds as if a character is in clear terrain and an attacker draws a line of fire on the character with stealth that crosses an unoccupied terrain of hindering then the attacker wouldn't be able to make the attack because instead of adding a +1 to the defender's defense, the stealth ability would cause the defender to be stealthed and unable to be shot, outwitted, perplexed, or probbed, despite being in clear terrain. Can someone help explain that to me. I always thought that stealth only activated when the character occupied hindering terrain. I might be over thinking this or reading it wrong, but please clarify that for me.

"...any line of fire that crosses Hindering Terrain..." pretty much explains it. If the line of fire crosses a square of Hindering Terrain, even if the figure with Stealth showing is not in/on a square of Hindering, then Stealth activates, and no line of fire may be drawn to that character.

Huh. Didn't realize that about the stealth typed powers. Might change some of my strategies. Thanks Bigbro for answering so fast. Rep to you.

The only real reason to place a Stealth character in hindering terrain is so that any LOF drawn to it must cross hindering terrain (meaning, no flanking the character to get around Stealth).

Otherwise, just placing a Stealthed character in hindering terrrain for the sake of doing so only results in a half-move penalty when you want to leave said terrain. If you can keep your Stealthed character out of hindering terrain while still maintaining a solid cover, do so. That way it can use its full movement.

To add to what Normalveiw said another reason to put a stealth character in hindering terrain is so that a character that is on elevated terrain cannot see OVER the hindering to make an attack against your stealthed charater.

Both Giants and Colossal characters do not ignore hindering terrain when drawing LOF (barring special rules in some of the Colossal scenario rules, of course).

From the Danger Room rule book (pages 50 and 51):

Standard-sized characters do not block line of fire to or from a giant character. Colossal characters and giant characters block line of fire to or from a giant character. Hindering terrain, blocking terrain, and elevated terrain affect line of fire to a giant character as normal. A grounded giant character and a grounded character draw line of fire and make ranged combat attacks against each other as if they were both grounded.

and

A character with the [colossal] damage symbol is a colossal character. Colossal characters are exceptionally big, and they may have special rules that are provided with the figure. Colossal characters do not halve their range values when attacking soaring characters. All colossal characters block lines of fire to other characters. Colossal characters ignore the effects of hindering, elevated, and outdoor blocking terrain on movement. Colossal characters cannot be moved by Telekinesis. Colossal figures may make ranged combat attacks when adjacent to opposing figures.

(note, in the case of colossal characters, while it does not specifically say they do not ignore hindering terrain for LOF, it also does not say that they do. And when special exceptions to general rules are not granted, you follow the general rule.)

Elevated LOF can, indeed, "peak" over hindering terrain to draw LOF to a Stealthed character sitting in clear terrain behind it, though.

Danger Room rule book (page 37):

An otherwise clear line of fire between an elevated character and a grounded character is blocked by giant characters and colossal characters; hindering terrain does not affect a line of fire drawn between an elevated character and a grounded character unless the target occupies a square of hindering terrain.

another good reason to be in hindering to use stealth is not just for elevated figs, but for TK or RS or HSS attacks that might get past the interveining hindering. If you are really worried about cutting your move in half, feat up with Running Start or stop on a stepladder. It is hindering for LoS only!

Thanks Normalview, I'll edit my post.

I prefer Swingline since it adds +1 to your bootspeed and that can be applied to HSS, Charge, as well as anything that involves the boot symbol.