How does opponent play more than one card per turn?

As the title of the thread says, "How does an opponent play more than one card per turn?" This does not include cards that reproduce. I mean something like a Nightcrawler and Captain America. Any insight here would be helpful. This is driving me crazy.

They use their turn 4 set of 4 energy and play the 1 energy cost Nightcrawler and the 3 cost Captain America, on turn 6 you could play six different 1 cost cards.

Thanks. That explains alot. I wish the instructions/help was a little better, but a cool game.