Suggestions by @thecrimsonpaw

Mike Mitchell

as Director in The Emperor’s New Groove

Lin-Manuel Miranda

as Theme Song Guy in The Emperor’s New Groove

Michelle Gomez

as Yzma in The Emperor’s New Groove

Julian McMahon

as Gallaxhar in Jimmy Neutron: Boy Genius

Martin Short

as Ooblar in Jimmy Neutron: Boy Genius

A.J. LoCascio

as "Starting My New Adventures..." in Superman: In Brainiac's Grasp.

Captain N

as "Starting My New Adventures..." in Superman: In Brainiac's Grasp.

Spoiler

as "Starting My New Adventures..." in Superman: In Brainiac's Grasp.

Russell Crowe

as King Goobot in Jimmy Neutron: Boy Genius

Jimmy Neutron: Boy Genius

as Next Project: in The Super Mario Bros: Invasion of the Koopa Kids.

Matt Shakman

as Director in The Super Mario Bros: Invasion of the Koopa Kids.

Julian McMahon

as "Commence the Invasion of Earth..." in The Super Mario Bros: Invasion of the Koopa Kids.

Gallaxhar

as "Commence the Invasion of Earth..." in The Super Mario Bros: Invasion of the Koopa Kids.

Spoiler

as "Commence the Invasion of Earth..." in The Super Mario Bros: Invasion of the Koopa Kids.

Willem Dafoe

as "Bring me Plan B..." in The Super Mario Bros: Invasion of the Koopa Kids.

Pedro Pascal

as "Bring me Plan B..." in The Super Mario Bros: Invasion of the Koopa Kids.

Waluigi

as "Bring me Plan B..." in The Super Mario Bros: Invasion of the Koopa Kids.

Wario

as "Bring me Plan B..." in The Super Mario Bros: Invasion of the Koopa Kids.

Spoiler

as "Bring me Plan B..." in The Super Mario Bros: Invasion of the Koopa Kids.

Koopa Kid

as Koopa Kid in The Super Mario Bros: Invasion of the Koopa Kids.