In a normal role-playing campaign, you only have to come up with an actual plot hook every dozen sessions or so. Not only will it takes several sessions to deal with the main plot, but there could be a B plot, side adventures, repercussions to slap the characters when they least expect it, and tangents to go off on because the players can't stay on the damn map. And that's all wonderful if you have the same people on a regular basis.
You are most likely playing this game because that is not the case.
When you constantly drop characters into a whole new scenario, in which they have no background from which to draw from, how do you get them into the plot?
We learned from play-testing that teenagers, even teenage heroes, even teenage heroes played by middle-aged adults, will not reliably involve themselves in other people’s problems. There would have to be some contrivance to drag them, kicking and screaming if necessary, into adventure and peril for the Greater Good - or even to just further the plot.
The answer, because we are Americans, was reality television, which is filled with people who should know better charging into contrived peril and humiliation for entirely selfish reasons. This is a game about a cartoon show about a game where teenage superheroes must meet ridiculous challenges in order to keep playing.
The Challenges are issued by the Producers, unseen, chaotic and perhaps insane gods, whose meddling in the fabric of space and time has made this all possible. The central goal of the challenge is to force the cast to do amusing deeds.
Challenges do not have to serve a particular useful or positive purpose. They do not have to be Good Deeds. Sometimes they are, and that's OK. But sometimes, they are just amusing.
Challenges are never, in contrast, harmful or destructive. The Cast cannot be challenged to do Bad Things. In particular, they should not be challenged to betray their core principles. That's just mean. In pursuing a challenge, a situation may arise that forces a hard moral decision of some sort, but that situation should not be mandated by the challenge itself. The Producers may be capricious, but they are not vindictive.
We have concocted several basic challenge templates, and even organized them into a table by desired frequency over the course of a season. You can choose one, of course, or roll 3d6, and let the dice choose for you.
If you don't like the roll, just re-roll. If you still don't like the roll, try combining the results.