Cartoons and Nicktoons/Random! Cartoons

Mr. Krabs the Unbearable

 * Mr. Krabs (from SpongeBob SquarePants) as Ivan the Unbearable
 * Sandy Cheeks (from SpongeBob SquarePants) as Ma
 * Stromboli (from Pinocchio) as Filthy Viking
 * Mordecai (from Regular Show) as Olaf
 * Squidward (from SpongeBob SquarePants) as Bjorn
 * Mr. Blik (from Catscratch) as Working Troll 1
 * Muscle Man (from Regular Show) as Working Troll 2

Bubbles and Hanazuki

 * Bubbles (from The Powerpuff Girls) as Sparkles
 * Hanazuki (from Hanazuki: Full of Treasures) as Gloom (Both have same voice)
 * SpongeBob (from SpongeBob SquarePants) as The Leprechaun
 * Princess Morbucks (from The Powerpuff Girls [1998]) as Pixie
 * Gil (from Bubble Guppies) as Little Prince
 * Mr and Mrs. Turner (from The Fairly OddParents) as Mom and Dad
 * Master Frown (from Unikitty!) as Munchie
 * Doug Dimmadome (from The Fairly OddParents) as The Announcer
 * Winslow (from CatDog) as Zit
 * Bloo (from Foster's Home for Imaginary Friends) as The Applause Fish
 * Pinkie Pie (from My Little Pony: Friendship is Magic), Jane Doe (from Camp Lazlo) and Lola Bunny (from Looney Tunes) as The Fuzzy Animal Gang

Mind the Pony

 * Fluttershy (from My Little Pony: Friendship is Magic) as Tabby
 * Applejack (from My Little Pony: Friendship is Magic) as Tabby's Mom
 * Darwin (from The Amazing World of Gumball) as Punky (Both look related)
 * Sanjay (from The Fairly OddParents) as Duck (Both have same voice)
 * Ren Hoek (from The Ren and Stimpy Show) as Lemurman

Creature Town

 * Mike Wazowski (from Monsters Inc.) as Lance
 * Patrick Star (from SpongeBob SquarePants) as Zoopie

HandyRabbit

 * Cream the Rabbit (from Sonic the Hedgehog/Sonic X) as HandyCat (I know Cream is female)
 * Cheese the Chao (Sonic the Hedgehog/Sonic X) as Drillbit (Both pets to HandyCat and Cream)
 * Madame Foster (from Foster's Home for Imaginary Friends) as Old Woman

Kingdom Hearts Time (Pilot)

 * Sora (from Kingdom Hearts) as Pen the Human (Old Finn)
 * Goofy (from Mickey Mouse) as Jake the Dog
 * Rainbow Dash (from My Little Pony: Friendship is Magic) as Rainicorn
 * Hello Kitty (from Growing Up with Hello Kitty/Hello Kitty's Paradise) as Princess Bubblegum (Both have beady eyes)
 * Dr. Eggman (from Sonic the Hedgehog/Sonic X) as Ice King
 * Sea Monster (other Cyclops) (from SpongeBob SquarePants) as Ice-Clops
 * Pooh (from Winnie the Pooh) as Snow Golem
 * Eeyore (from Winnie the Pooh) as Old Man
 * "Yeah! What?" Ghost (from Growing Up with Hello Kitty) as Fire Element
 * Abraham Lincoln as Himself (Adventure Time [Pilot] itself)

Stimpy and Eddy

 * Stimpy (from The Ren and Stimpy Show) as Bronk
 * Eddy (from Ed, Edd n Eddy) as Bongo
 * Sonic the Hedgehog (from from Sonic the Hedgehog/Sonic X) as Geezer (doctor)
 * Grim Reaper (from The Grim Adventures of Billy and Mandy) as The Skeleton
 * Billy's Dad (from The Grim Adventures of Billy and Mandy) as The Patient (Both look related)
 * Brandy Harrington (from Brandy and Mr. Whiskers) as The Dinosaur
 * Edward (from Camp Lazlo) as Ted Strawberry Head
 * Commander Hoo-Ha (from Camp Lazlo) as The Workman

ThomBall

 * Gumball (from The Amazing World of Gumball) as Thom Cat
 * Anais (from The Amazing World of Gumball) as Melissa
 * Snowball (from Battle for Dream Island) as Rusty
 * John Smith (from Pocahontas) as Neighbor John
 * Gordon and Waffle (from Catscratch) as Stumpy and Pat