I am new to Heroclix and I am really confused about Outwit.

First question: Can Outwit only be used once per turn?

Second question (err... statement): I need some clarification on what Outwit can't counter. I know that it can only counter possessed powers, but I'm not 100% sure what defines a possessed and a used power. Some specific examples that I need clarification on are:
-Can Outwit counter power action abilities such as charge and running shot?
-Example: "Watching Your Backside Nightwing and Batgirl can use Combat Reflexes and Super Senses." So that means Combat Reflexes and Super Senses would be used powers and therefore cannot be countered by Outwit, right? Could you counter the ability "Watching Your Backside" instead and counter both at once?

A single character can only use Outwit once per turn, unless they have something on their card that says otherwise.

A possessed power is a power showing on the dial, or if a description says "character A has power X". Has = possession. Can use just means they can use it, and the power can't be countered. But, if its a possessed power that says they can use a power, you can Outwit the possessed power, thereby eliminating the "can use" power.

In your example: You can Outwit the entire power "Watching Your Backside". You cannot counter the powers Combat Reflexes and Super Senses. Looks like you were thinking that way, and you were correct.

Yes, once per turn - you GIVE an Action to Outwit.

Page 18 of the rulebook covers USE vs Possess

It can counter the Powers not the Actions

Yes, exactly this.

Thanks! I really don't know what was so hard about me understanding used and possessed powers, or for that matter, anything I asked. I will definitely be using these forums again in the future for (common sense) questions because they get answered so quickly.

Just a slight add on.. Outwit is a 'Free Action'

When a special power grants the use of multiple powers, as they often do, you cannot outwit the granted powers but you can outwit the granting power and prevent the character form using either

Each character on your team that has use of the power, either directly (i.e. their damage slot is black) or indirectly (i.e., they have a special power that includes the words "can use Outwit") use Outwit once per turn, after you have given them a free action to do so

One thing Outwit can do that a lot of people forget about is counter combat abilities. This means you can take away someone's ability to carry, or a flyer's ability to ignore terrain while moving, etc. Improved Movement and Improved Targeting are also combat abilities and can be Outwitted.

This is an important point. Outwitting Sharpshooter or Indomitable at the right time can change the game.