On their second click, the CW chase duo Doom/Kang has the following special power:
AFTER ULTIMATE POWER - Give Dr. Doom and Kang a power action. Place them adjacent to the highest point opposing character on the map, then use the Duo Attack ability as a free action targeting that character for each attack.
Steal Energy reads:
Steal Energy - Each time an opposing character takes damage from a close combat attack made by this character, heal this character of 1 damage.
(SE wording might not be the latest, I copied it from an app...iPod Internet and whatnot)

My question is this:
Doom/Kang activates the SP in click #2, either after pushing or taking damage. They have the IG with the Soul Gem showing, granting them Steal Energy. They attack, using the duo attack ability as described above. The attack success and the target takes damage. Doom/Kang heal back to click one.
All this so far is fine. But where I wonder is the next part. Can Doom/Kang make the second attack granted by Duo attack? They still possess the ability itself, but they no longer possess the power that granted them an (abnormal) use of that ability.

I would say that they have to resolve the currency action. And since nothing in duo attack states that the action cannot continue if the power is lost (a la HSS/Flurry), them the action continues. They would make the second attack, right?

Actually, Duo Attack does state that: "If this character is defeated or loses Duo Attack as a result of the first attack, the second attack is not made."

Going by the old ruling where if you go from normal HSS to special HSS the action ends, I would say that the second attack can't be made in this situation.

They may lose the special power, but they still have the duo attack ability. You can make the second attack.

Ah, I probably should've quoted Duo too. Alrighty then. Unfortunate.

This is the very true part, however. They do not lose Duo Attack just because the special power isn't showing.

Side note:
This part means they can use Duo Attack during this power even if they've betrayed each other and now have . THEN if they lost the power they wouldn't be able to make the second attack

But the duo attack was activate by a power that is no longer there. And since Duo does state that if it's lost you can't complete the action, then you can't. I agree with VP that this is similar to HSS and SP HSS. Or Outwit and SP Outwit.

Duo does say that. Does the figure lose Duo attack?

No. But they lost the power that allowed them to make the duo attack that they ordinarily wouldn't. Ergo, the HSS/HSS-SP example hits closest to home in my mind.

I wouldn't mind this being wrong, but I don't know, that's why I asked.

I'd say this is more like using the first free action of Multi-attack to switch from SnV to Void and then making the second attack. The power is gone, but the power action isn't complete: you finish the power action.

*in the interest of full disclosure I've had several *POP* moments in the past few days on rules issues, so take my input with due caution.

Provided they can actually still use Duo Attack normally (you haven't yet hit Inevitable Betrayal), I see no reason why they couldn't keep using the Duo Attack. All this power really does is let them use an ability they could already use as a free action instead of a power action; there really is no way for them to "lose" Duo Attack.

Yeah, that was the reference in favor of it working that I had in my head, too.

Thanks normalview. Good to know!