Nosferatu Zodd's Apostle Form (Berserk)
Grunbeld's The Great Flame Dragon Apostle Form (Berserk)
D-Struct (Static Shock) in his monster form.
Tamra Lawerence (Static Shock) in her beast form.
Wayland Jones/Killer Croc (DC Comics)
Monster Society of Evil (DC Comics)
Tony Tony Chopper (One Piece) in his Monster Point form.
Due to being experimented on with Dark Eco for two years, Jak (Jak and Daxter) can transform into "Dark Jak".
Kevin Levin (Ben 10) often takes on the form of a monstrous, chimeric fusion of aliens when he absorbs energy from the Omnitrix/Ultimatrix.
Like his father Devlin Levin (Ben 10) has the ability...
... to transformed into kevin 11.
Since he escaped Kevin 11,000 (Ben 10 series) as human has the ability...
... to transformed intro kevin 11,000 after he absorbed the power of the other aliens.
Omniverse Kevin (Ben 10: Omniverse ) in his mutation form.
Kevin's Flashback Mutation (Ben 10: Omniverse) in his mutation form.
Monster Kevin (Ben 10 Reboot)
Joseph Bertrand III (Infamous) in the form of the Behemoth.
Vegeta (Dragon Ball Z) in his Oozaru/Great Ape form.
Zarbon (Dragon Ball Z) in his monster form.
Kimimaro (Naruto) when he activates the Cursed Seal of Earth.
Sasuke Uchiha (Naruto) when he activates the Cursed Seal of Heaven.
Jūgo (Naruto) transforming.
A mass amount of Cursed Seal users (Naruto) going berserk.
Kaguya Ōtsutsuki (Naruto) turning into a monstrous form when she lost control of her powers.
Tosen (Bleach) releasing his Resurreccion, Grillar Grillo, to transform into a gigantic cricket Hollow.
Sora (Kingdom Hearts) in his Anti-Form.
Sora's (Kingdom Hearts Series) Monster form in the Monsters Inc. World.
Daxter (Jak and Daxter) can transform into "Dark Daxter" due to further exposure to Dark Eco.
Richard Wilkins III (Buffy the Vampire Slayer) in the form of the snake demon Olvikan.
Ninja Turtles (Teenage Mutant Ninja Turtles; 1987 TV series) in their super mutant forms.
Carter (Teenage Mutant Ninja Turtle; 1987 TV series) can transform into a yellow skinned creature with super-strength due to exposure to Mutagen.
Xion (Bloody Roar) in the form of the Unborn.
The monstrous Giga Bowser (Super Smash Bros.)
Ganondorf Dragmire (The Legend of Zelda) in his beast form, Ganon.
Vincent Valentine (Compilation of Final Fantasy VII) in the form of Chaos.
While under the influence of a full moon, Untrained Saiyans (Dragon Ball series) transform into feral Oozaru/Great Ape.
Goku (Dragonball Evolution) transforms into the monstrous Oozaru under a solar eclipse.
Sonson (Marvel vs. Capcom 2) can temporarily take on a more monstrous monkey form.
Cadence Nash (The Troop) is a human/Blood Thrasher hybrid, and can assume her Blood Thrasher form at will.
Kaine (Marvel Comics) as the monstrous Tarantula.
The SA-X (Metroid Fusion) in its monster form.
Mohinder (Heroes) slowly transforms into an insect monster.
Elfman strauss (Fairy tail) takes on a monstrous form
The Thing Monster (John Carpenter's The Thing)
Gear REX (Metal Gear Solid: Peace Walker)
Monsters (Monsters, Inc.)
Calvin Dion Avericci (Archie's Weird Mysteries) is a shopaholic so greedy, he sold his soul to keep buying, resulting in his demonification.
As a Lummox, Riki (Saga Frontier) has the ability to transform into and use the traits of any and all monsters.
Letting the Ghost ÄRM, Hydra erase whatever humanity was left in her heart, Chimera (Marchen Awakens Romance) succeeded in obtaining the ÄRM’s power. Deprived of human feelings and sharing Hydra’s horrific body, Chimera had truly become a monster.
Green Goblin (Spider-Man: Into the Spider-Verse)
Kyo Sohma (Fruits Basket) in his monster form.
Jonathan Rook/Stretch Monster (Stretch Armstrong and the Flex Fighters)
Multi-Farious (Stretch Armstrong and the Flex Fighters)
The Violator (Image Comics) in his true form.
Pyscho Rangers' Monster Forms (Power Rangers)
Monsters (War of the Monsters)
Team Monster (Monsters vs. Aliens)
Monsterex (Teenage Mutant Ninja Turtles Adventures)
Bloodwork's Monster Form (Arrowverse)
Guardian (The Real Adventures of Jonny Quest)
Frankencreep (Scooby Doo! Frankencreepy)
Herbert Landon (Spider-Man: The Animated Series)
Mogowki (Famous 5: On the Case)
Dust Devil (Pebbles, Dino and Bamm-Bamm/The Flintstone Comedy Show 1980/Hanna-Barbera)
Dr. John Whitney/Kothoga (The Relic)
Muscular Creature (Captain Caveman and the Teen Angels/Hanna-Barbera)
Mole Monster (Archie's Weird Mysteries Comics)
Leaf Monsters (Archie's Weird Mysteries Comics)
Werewolf, Robot and Fly Trap Monster (Martin Mystery)