Suggestions by @batboy1999

Woodstock

as Cameos in Phineas and Ferb

Snoopy

as Cameos in Phineas and Ferb

The Brain

as Cameos in Phineas and Ferb

Pinky

as Cameos in Phineas and Ferb

Dot Warner

as Cameos in Phineas and Ferb

Wakko Warner

as Cameos in Phineas and Ferb

Yakko Warner

as Cameos in Phineas and Ferb

Runt (Animaniacs)

as Cameos in Phineas and Ferb

Rita (Animaniacs)

as Cameos in Phineas and Ferb

Harold Ramis

as Sam McGuire in Lizzie McGuire (1981-1984)

Morty Smith

as Cameos in Frying Nemo

Zipper (Disney)

as Cameos in Frying Nemo

Monterey Jack (Disney)

as Cameos in Frying Nemo

Chip 'n' Dale

as Cameos in Frying Nemo

Monty Python

as The Three Stooges in Most Wanted Crossovers

Nostalgia Critic

as Cameos in Frying Nemo

Grover (Sesame Street)

as Cameos in Frying Nemo

Runt (Animaniacs)

as Cameos in Frying Nemo

Rita (Animaniacs)

as Cameos in Frying Nemo

Zendaya Coleman

as Alison Brie in Dream Actor / Actress-Actor / Actress Collaborations