CHAMPION AND STEED: Once per turn, when an opposing character has taken damage from his attack, give Tiamat any action as a free action. When you do, after action resolve, remove an action token from Tiamat.

Now if I mind control a friendly Tiamat, can I take the free action with him if I hit then attack normally with Tiamat and get the free action again on hit since the once per turn action was taken while mind controlled?

No when you mind control you get 1 action as a free action, if you were to sidestep as a free action thats your action

But you can give Running Shot, Charge, Hypersonic Speed, Duo Attack, etc actions which include nested free actions and Tiamat seems to allow himself a free action during the other action as opposed to waiting until after it resolves.

I would say Tiamat can take the action.

It says "when an opposing character has taken damage from his attack". It doesn't say "after actions resolve, give him a free action". So yea, I think I have to agree with A_B, it happens before actions resolve, meaning the MC is still in effect.

I, too, agree with A_B

But would I get to do this again after a Mind Control similar to how you can do Once per Game actions twice with a friendly Mind Control

The issue is, the default rule is you can't use another action until the first one resolves. This is why you can't running shot, outwit, and attack in that order. Outwit doesn't say 'after actions resolve'.

Assuming each time a different character Mind Controlled Tiamat, yes.

No, but Outwit also doesn't trigger based on a "when" condition. A better example is steal energy. Do you wait until actions resolve to heal 1 click or do you do it when it is triggered, interrupting current actions?

And the rule you are referencing:

States that resolving an action includes resolving the free actions that action allows. That's why you can Charge during Mind Control and still get to make the attack.

I miss the old MC that used to give your opponents action tokens. One of my favorite tricks was using Prof X to mind control my opponents Wild card figure who was usually based with my other X-men and give my opponent an action to copy X-men TA and heal my guy, take a click of damage, and take a token as well. Ah the good ol' days!

Steal energy is not an action
The close combat action is part of charge.
Charge is not part of hypersonic speed. (Though if that is how this works, it makes him even more awesome since he could HSS, charge, and then retreat without breaking away with the rest of his HSS movement).

I don't understand what you are trying to say.

Steal Energy is non optional and does require a character to make an attack that deals damage before it triggered.

When one uses HSS the whole action needs to resolve move, attack, move away then he gets to use the free action to do something else. Generally what one wants to do with a figure like that is Charge, Flurry, and then K.O. the opposing character in one turn oh, and now he's got only one action token so he's free to do the the same thing turn after turn without end.

My post was in reply to someone else saying free actions happen in the middle of an action. There is a long held stance that unrelated free actions must wait until after an action resolves, but you are explaining this in response to my post as if I wasn't the only one in this thread who actually agreed with what you just posted.

This is incorrect.

Tiamat will:
Declare power action to use HSS
Move
Attack
If it hits and the character takes damage, champion steed will trigger
Take the free action
Finish moving for HSS
Action is resolved

Anything official on this yet?