This article is for the different forms that Penn Zero takes on missions in different dimensions.
Forms are sorted in the alphabetical order of the worlds, with unknown/unnamed worlds listed at the bottom.

Normal appearance 

Penn Zero

Penn Zero's normal appearance.

When not zapped into another dimension, Penn is normal height, thin, young high-schooler. He has curly red hair, cyan eyes, and two front teeth that appear bigger than the others. He wears a long sleeve shirt with blue plaid cuffs and collar, a white, orange-outlined null sign on his chest. He wears chain mail underneath his shirt that sticks out of his sleeves and collar. He also sports red skinny jeans, white and black shoes with a gold horizontal stripe along the ankle, and a black-colored belt with the MUHU.

Alien World

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Penn Zero's Arabian appearance.

In Alien World, Penn replaces an alien from the Purple People.

Animal Barbarian World

In Animal Barbarian World, Penn replaces a Rabbit barbarian leader.

Anime World

In Anime World, Penn replaces a karate man who is part of the 5 ninja warriors.
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Penn Zero's Animal Barbarian appearance.

Arabian World

In Arabian World, Penn replaces a magic carpet rider who has the magic lamp.

Ball World

In Ball World, Penn replaces a tennis ball. Being a ball, Penn rolls around and can bounce. On the other hand, he doesn't have arms or legs, forcing him to use his teeth to hold a tennis net while trying to save 8 Ball.

Blackhole World

In Blackhole world, Penn replaces a Mouse.

Body World

In Body World, Penn was supposed to replace a scientist but instead replaces an ill patient when he accidentally switches places with Boone.

Cereal World

In Cereal World, Penn replaces Choco Chuck, the elephant cereal mascot of Choco Choco Choco Trunks. Like a normal elephant, Penn can use his trunk to suck up liquid and shoot it out.

Clown World

In Clown World, Penn replaces a clown policeman. Penn easily adapts to the clown logic and physics in this world.

Demon World

In Demon World, Penn replaces a normal person dressed in colonial attire.

Dinosaur Cowboy World

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Penn Zero's Dinosaur Cowboy appearance.

In Dinosaur Cowboy World, Penn replaces a cowboy. Penn is surprised and disappointed that he isn't the sheriff, losing excitement for the world. However, this changes when he finds out there are dinosaurs included with the cowboy.

Dragon World

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Penn Zero's Dragon appearance.

In Dragon World, Penn replaces a dragon student named Renegade.

Fairymania World

In Fairymania World, Penn replaces one of the wrestling members of a duo team called the "Wings of Destiny".

Ghost World

In Ghost World, Penn replaces a social worker ghost.

Galaxy World

In Galaxy World, Penn replaces a human with a metal suit.

Giant Monster World

In Giant Monster World, Penn replaces a giant lizard monster. Penn has the ability to breathe fire, though it makes it challenging for him to speak sometimes. In addition, his size gives him a lot of strength. He finds it challenging to not cause damage in this world with his fire breath or his size.

Gothic Mystery World

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Penn Zero's Gothic Mystery appearance.

In Gothic Mystery World, Penn replaces a professor and will transform into a Rippen monster when he is impatient.

Knight World

Penn Zero (Knight)

Penn Zero's Knight appearance.

In Knight World, Penn replaces a knight.

Man-Eating Burrito World

In Man-Eating Burrito World, Penn replaces a normal person.

Musical Fairytale World

In Musical Fairytale World, Penn replaces a princess. Penn doesn't mind being a girl, but he prefers being a tomboy than a girly-girl.

North Pole

Penn Zero (North Pole)

Penn Zero's North Pole appearance.

In the North Pole, Penn replaces Santa Claus. As Santa, he is overweight, and he has light gray curly hair with a beard. He wears a red hat with white lining on the edge and the tip, a red coat and pants with white lining on the sleeves, a black belt with a golden buckle, and black boots. Being Santa, Penn is able to go through any chimney, though he has to be going with a sack to put a present under a tree. Despite taking on the role, Penn is initially disappointed, not wanting anything to do with Christmas because his parents aren't there, so he just wants to get the mission over with. But when Christmas is at stake, Rippen forcing Penn to chose between saving the MUHU and saving Christmas, Penn sadly chooses the other and loses the MUHU.

Ocean World

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Penn Zero's Ocean appearance.

In Ocean World, Penn replaces the prince of the merpeople. As the prince, Penn is the only one able to use the magic trident, which can create powerful whirlpools and waves. As a merperson, Penn can breathe underwater and swim, though he is still able to breathe and move on land. His webbed hands also create huge blasts when he high-fives someone.

Old English World

In Old English World, Penn replaces an actor from a theater troupe.

Outer Space Court World

In Outer Space Court World, Penn replaces the president of the United States of America. Penn finds being president cool, though isn't allowed to do anything fun by Sashi, telling him his role is to sign bills from the legislation.

Plush Toy World

In Plush Toy World, Penn replaces a cheapo carnival prize plush dog. Penn's arms can be easily pulled off or cut off his body, much to his annoyance. In the episode "The Chinchilla", Penn gets his arm eaten by a giant "The Chinchilla" and replaces it with a crab arm he finds at Dr. Hissy's office.

Plant World

In Plant World, Penn replaces a Cactus detective.

Sitcom World

In Sitcom World, Penn replaces the dad called Mr. Wright.

Space World

Penn Zero (Space)

Penn Zero's first Space appearance.

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Penn Zero's Flurgle appearance .

In Space World, Penn replaces the admiral on a spaceship. Due to Sashi accidentally shooting the Flurgle into Penn's transporting tube while transporting from the ship to a planet, Penn gets fused with the Flurgle. Combined with the Flurgle, Penn is easily distracted and acts very dog-like in behavior.

Steampunk World

In this world, Penn is an automoton built by Boone and is golden with a top hat and gears. He also has green eyes. He has a wind-up key on his back to serve as a power source. He also has boxing gloves, paper-fan shields, a cuckoo clock, a croissant, and sick break dancing skills. If he sets the Cuckoo clock to 3:00 the bird will come out with boxing gloves.

Superhero World

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Penn Zero's Superhero appearance.

In Superhero World, Penn's favorite world to visit, he replaces a superhero. Penn has many superpowers, including super strength, flight, laser vision, and a great wink. Hoping for this world for ages, Penn is excited to visit it and just as thrilled to return to it.

Temple World

In Temple World, Penn replaces an adventurer. Penn struggles to keep his man-purse closed shut in this world.

Ultrahyperball World

In Ulrahyperball World, Penn replaces a tarbgarbs player.

Zombie World

In Zombie World, Penn is a fast food worker. Penn, not knowing the mission, is relieved by having a normal job. Getting bored, he complains until discovering in horror that there are zombies in this world.

Other unknown worlds

  • In the theme song, Penn replaces a:
  • Penn replaces a viking (seen in the poster).