Here are some good one act plays for a superhero themed show:
Superhero Support Group: 6 actor one act about heroes in need of therapy http://www.freedrama.net/supers.html
Super Dead Man: 7 actor one act about the villain who finally defeats a superhero http://freedrama.net/superdead.html
Protecto (kid hero): monologue about a kid who wants to be a hero http://freedrama.net/protecto.html
Then perform these improv games between each one act play:
Defeat the Superhero League: One actor is a super villain. Three or four actors pick superheroes they want to be but keep their identify secret from everyone. Each superhero bursts in to the villain's secret lab. The actor must act like their hero but can't say their name. The villain must guess who they are to defeat them and get keep them from destroying the secret lab. If the villain doesn't guess in a few minutes, another superhero enters. When all the heroes are present and have a chance to show their powers, then the villain must guess who they are (within a time limit) or be defeated.
Gibberish: A group of actors (group #1) are superheroes from another world and act out a scene speaking in a weird alien language. They act out a simple activity like playing baseball or cooking. The other group of actors (group #2) act out the same scene and translate what was said in English.
Variation: have actors translate what was said by the aliens as they act
Variation 2: have a actor play a superhero alien who speaks gibberish and have the other actors try to figure out what he/she is saying in a scene where an alien lands in their backyard
Press Conference: One actor volunteers to be the "famous person" from comic books or superhero movies. The actor becomes the famous person by acting the same as the person and using their voice or accent but can only answer yes or no. The other students interview the "famous person" and they get yes or no answers until they can guess who it is.
Superhero Story in a Minute: The actors get a superhero story title from the audience and then act out the story in one minute. Then they must act out the same thing in 30 seconds. THEN they must act it out in 10 seconds.
Stunt Doubles: 2 Actors are acting a scene such as dealing with a villain who is doing something bad. When it comes time to do a "dangerous" step (such as punching the villain) they call in their stunt doubles. The easier the "dangerous" task is, the funnier it can be (such as picking up litter).
Lines from our Pockets: The audience will write lines for the actors to say. Someone will collect the lines and not show them to the actors. The actors will act out a superhero scene and then they must work the lines into the scene.
Here Comes Superfly: One actor plays Superfly who is off stage. The other two actors are two citizens who need help. The two citizens are disappointed to see Superfly coming and describe the terrible things Superfly does while he/she is off stage. Superfly enters to try and help and she has to act like she is described.
Evil Inventions (aka props): All the actors are super villains. Give the villains weird things they have never seen before and they must say what they do. The object can do anything except what it really does.
Questions Only: Actors get in two lines (one line is villain and the other is heroes). They talk in the form of a question. If they make a statement or don't use a question, then they must go to the back of the line or the audience can shout DIE and they must do a dramatic death scene. The line with the most left at the end wins.
Stand Sit Slump: A superhero faces two villains (or two heroes face one villain). One must be standing, one must be sitting and one must slump down on the ground. After each actor says one thing, the last actor to speak must pick a new position (stand) and the others must adjust and pick the two remaining positions (sit and slump). This can continue until a high moment of humor or until one actor messes up.
Pick your Superhero (The Good, the Bad, and the Ugly): You must pick a superhero to join your League of Just Avengers. 3 players (superheroes) form a line upstage. The audience provides questions or problems for which they need advice. Actor #1 always provide good advice, actors #2 always gives bad advice , and actors #3 gives really bad advice. Good advice should be good, bad should be opposite of the good and ugly should be an even worse version of bad.
Action Figures: 1-2 actors are superhero action figures and 1-2 actors are villain action figures. They must do battle but none of them can move on their own. They can only speak. 2 audience members must move them in to battle.