Nicktoons/Marvel

Heroes and Anti-heroes

 * Timmy Turner/Arachnid-Kid as Peter Parker/Spider-Man (watch Abra-Catastrophe; in Ultimate Spider-Man, Peter is voiced by Drake Bell, who played Timmy in A Fairly Odd Movie)
 * Dudley Puppy/Iron Mutt as Tony Stark/Iron Man (watch T.U.F.F. Puppy's Iron Mutt episode)
 * Keswick as James Rupert Rhodes/War Machine
 * Jimmy Neutron/Hulk Jimmy as Bruce Banner/Hulk (watch Jimmy Neutron's The N-Men episode)
 * Tommy Pickles as Steve Rogers/Captain America (Both are good leaders)
 * Chuckie Finster as Bucky Barnes/the Winter Soldier
 * Otto Rocket as Sam Wilson/Falcon
 * SpongeBob SquarePants as Thor Odinson (SpongeBob is from a different world)
 * Tuesday X as Natasha Ramanoff/Black Widow
 * Dib Membrane as Clint Barton/Hawkeye
 * Bolin as Pietro Maximoff/Quicksilver
 * Avatar Korra as Wanda Maximoff/the Scarlet Witch
 * Fugitoid as Vision
 * Manny Rivera/El Tigre as T'Challa/the Black Panther
 * Shinigami as Ororo Iqadi T'Challa/Storm
 * Leonardo as Scott Summers/Cyclops
 * Hamato Miwa/Karai as Jean Grey-Summers/Pheonix
 * April O'Neil as Anna Marie Darkholme/Rogue
 * Raphael as Logan Howlett/Wolverine
 * Donatello as Hank McCoy/Beast
 * Michelangelo as Bobby Drake/Iceman
 * Casey Jones as Kurt Wagner/Nightcrawler
 * Y'Gythgba as Angelica Jones/Firestar
 * Hamato Yoshi/Splinter as Professor X
 * Ren Hoek as Wade Wilson/Deadpool (Both are wild, crazy, and inappropriate)
 * Stimpson J. Cat as Weasel
 * Alopex as Ellie Phimister/Negasonic Teenage Warhead
 * Leatherhead as Piotr Rasputin/Colossus
 * Doug Funnie/Quailman as Scott Lang/Ant-Man
 * Mr. Dink as Hank Pym
 * Bessie Higgenbottom/the Mighty Bee as Janet van Dyne/the Wasp
 * Avatar Aang as Doctor Stephen Vincent Strange
 * Jorgen Von Strangle as Nick Fury
 * Binky as Phil Coulson
 * Mrs. X as Maria Hill
 * Ginger Foutley as Peggy Carter
 * Kimi Finster as Sharon Carter
 * Pig as Ben Grimm/the Thing
 * Goat as Sue Storm/the Invisible Woman
 * Banana as Johnny Storm/the Human Torch
 * Cricket as Reed Richards/Mr. Fantastic
 * Sleazy Beave/the Masked Maniac as Norrin Radd/Silver Surfer
 * Jenny Wakeman/XJ-9 as Carol Danvers/Ms. Marvel
 * Danny Fenton/Danny Phantom as Johnny Blaze/Ghost Rider
 * Arnold Shortman as Matt Murdock/Daredevil (they both 'lost' a relative)
 * Helga Pataki as Elektra Natchios
 * Ickis as Frank Castle/the Punisher
 * Snap White as Eric Brooks/Blade
 * Reptar as Ted Sallis/Man-Thing
 * Sheen Esteves as Peter Jason Quill/Star-Lord
 * Aseefa as Gamora
 * Doppy as Drax the Destroyer
 * Mr. Nesmith as Rocket Raccoon
 * Crock Crock as Groot
 * Stick Stickly as Howard the Duck

Villains
More ideas?
 * Vlad Masters/Vlad Plasmius as Norman Osborn/the Green Goblin
 * Denzel Crocker/Crocktopus as Otto Octavius/Doctor Octopus (watch The Big Super Hero Wish)
 * Verminious Snaptrap as Obadiah Stane/Iron Monger
 * Armagedroid as Ultron
 * Professor Calamitous as Thunderbolt Ross
 * Meldar Prime as the Leader
 * Sheldon J. Plankton as Loki
 * Oroku Saki/the Shredder as Max Eisenhardt/Magneto
 * Pariah Dark as Mephistopheles
 * Fright Knight as Blackheart
 * Alphonse Perrier du von Scheck as Wilson Fisk/the Kingpin
 * Nick Vermicelli as Lester/Bullseye
 * The Gromble as Jigsaw
 * Dorkus as Ronin the Destroyer