Yes, same as any use of duo attack or flurry.

There's nothing in his power that hinges on 'making the first attack' any more than Duo or Flurry. His power allows him to do something extra prior to each attack.

As long as his first square allows him to attempt an attack it's legal. It's a given in the game that powers like Shape Change may prevent the attack from happening after it's declared.

He could do something like target terrain with the first of the duo attacks, then attack a character with the second.

Well, with their new ruling on attacking terrain, he may not be able to use it to jump.

Nothing about his power is triggered by a successful attack, which is what that ruling was about.

Right on. It was just a half thought.