When thinking about how outwit works now it was easy for me to get, "I'm outwitting Hulk's impervious" that he doesn't have now, but I know he will here in a second. I hadn't been thinking about outwitting special powers that will be coming up. In a game would you accept, "I'm going to outwit Hulk's special defense power" that he doesn't have now, but I know he will here in a second, or would I need to say "I'm outwitting Hulk's 'Fueled by anger' power"

There's nothing wrong with clarity.

As long as you're clear about what's being named. If the opponent wants you to use the actual name of the power, then just look at their card.