Fake Hero by Lucas Flint

Fake superheroes. Real comedy.

Doctor Mind has it made. Having spent the last three years using a combination of alien technology and clever stage magic to fool the people of Freedom City into thinking he's a legitimate superhero (including hiring his failed actor brother to play his supervillains), Doctor Mind thinks he's set for life.

Until a real supervillain, the dangerous but quirky Death Skull the Murderer, shows up and threatens to destroy the entire city in a month unless Doctor Mind defeats him in a fight.

Ostracized from the mainstream superhero community for his scammy business, Doctor Mind must recruit and train a team of superhero rejects—including a Canadian lumberjack with a personal vendetta against trees, a washed-out sidekick who looks like a baby despite being an adult, and a woman with more brawn than brains—to become real superheroes and save his city from Death Skull.

Assuming they don't kill each other first.