This article is for the different forms that Rippen 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

Rippen Model
When he isn't in another dimension, Rippen is tall and muscular with pale green skin. He has black hair with several greenish-gray streaks, along with a goatee, and he has red eyes and pointed ears. He wears a dark purple business suit with light gray sleeve ends and collar, a red tie, black pants with a black belt, and black shoes. When he's being an art teacher, he wears a gold-colored apron with paint smears and pockets to hold art supplies.

Alien World

In Alien World, Rippen replaces a Kronad.

Arabian World

In Arabian World, Rippen replaces a bandit.

Anime World

In Anime World Rippen appears as an evil chef.

Blackhole World

In blackhole world Rippen appears as a robot cat.

Ball World

In Ball World, Rippen replaces a tennis racket.

Body World

In Body World, Rippen replaces and evil doctor

Beast World

In Beast World, Rippen replaces an evil warrior king.

Cereal World

In Cereal World, Rippen replaces a cereal mascot named Wrong-Way Wally.

Clown World

In Clown World, Rippen replaces the criminal clown Farpling.

Demon World

In Demon World, because a sick Rippen takes the day off and Larry substitutes as the part-time villain, Rippen replaces a skeleton minion.

Only having a skeleton for a body, he is very fragile, getting crushed when Larry, in his muscular overlord form, hugs him.

Dinosaur Cowboy World

In Dinosaur Cowboy World, Rippen replaces a bandit.

Fairy World

In Fairy World, Rippen replaces "Collateral Damage" a member of the wrestling team called "The UnFairies".

Galaxy World

In Galaxy World, Rippen replaces a person with a metal suit.

Giant Monster World

In Giant Monster World, Rippen replaces a general of Island City.

Ghost World

In Ghost World Rippen replaces a ghost hunter

Knight World

In Knight World, Rippen replaces a goblin leader.

Least Dangerous World Imaginable

in Least Dangerous World Imaginable Rippen replaces a mayor

Musical Fairytale World

In Musical Fairytale World, Rippen replaces a sorceress.

As a sorceress, Rippen possesses magical powers, being able to transform trees into monsters.

Rippen finds it cool being a lady, commenting on how he likes his horns and lipstick, though he is not impressed with his dress and mascara.

North Pole

At the North Pole, Rippen replaces a gingerbread man.

Ocean World

In Ocean World, Rippen replaces the leader of the Octopus people.

In this form, he can swim underwater and breathe out of water.

Old English World

In Old English World, Rippen replaces Crossbow, a bandit.

His left hand is replaced with a mini crossbow, which he can use to shoot arrows.

Outer Space Court World

In Outer Space Court World, Rippen replaces an alien general named Ugthar the Ugly.

Plush Toy World

In Plush Toy World, Rippen replaces a giant baby.

With his size, Rippen is strong, easily able to grab a plane in mid-flight and beat the stuffing out of Mayor Pink Panda. Unfortunately, this doesn't prevent him from immediately being pacified after he is given a hug and a pacifier. As a baby, Rippen can't speak, but he still thinks fluently. But in The Chinchilla (episode) he becomes a toddler who can speak albeit in very few and simple words, 

Pirate World

In Pirate World, Rippen replaces evil pirate called Wood Beard.

Sitcom World

In Sitcom World, Rippen replaces a mischievous son named Max Wright.

Space World

In Space World, Rippen replaces an alien.

Superhero World

In Superhero World, Rippen replaces a super-villain with a robot suit.

The suit has multiple arms and lasers. It also has a chest compartment that stores Larry, who in this universe is a human parasite. Rippen can use Larry's ability to steal super powers, giving Rippen powers to choose from and use, like super strength, super speed, growth, electricity manipulation, etc. However, if Larry is detached, Rippen looses the powers.

Steampunk World

In Steampunk World Rippen appears as a fighting automaton.

Temple World

In Temple World, Rippen replaces an evil adventurer.

Ultrahyperball World

In Ultrahyperball world Rippen replaces a Ultrahyperball player

Zombie World

In Zombie World, Rippen replaces the owner the of Brainzburgerz restaurant chain. At the end, Rippen becomes a zombie after Zombie Larry forces a burger into his mouth.

Other unknown worlds