This act is all about rising actions and stakes, as the challenges get harder. This is where complications are revealed as The Problem grows and mutates.
This is also where the adversaries are going to make their moves, and adjust to the new threat posed by the Cast. No worthwhile villain should just stand there and wait to be caught. The smarter of the villains are going to take note of the Cast’s awesome displays from Act I and find ways to counter just that.
The action should escalate to the first big battle – an even match where foolish cast members could get clobbered or worse. The cast should survive (barring foolishness) but not prevail. Their initial plan (unless it’s really, really good) should lie in a smoking heap at their feet while The Problem rages on worse than ever. This realization is the end of Act II.
Commercial.