5 suggestions

Tohoru Masamune
as Shredder in What if the 2014 Teenage mutant ninja turtles movie was good?

Andy Serkis
as Old hob in Fancasting teenage mutant ninja turtles characters

Clancy Brown
as Mammoth in Fancasting teenage mutant ninja turtles characters
Keke Palmer
as Cassie in Animorphs

Gregory Smith
as Jake in Animorphs