Suggestions by @simonzilla

Benedict Cumberbatch

as Keizer Ghidorah in SimonVerse: The Series

J.K. Simmons

as Storm King in SimonVerse: The Series

Eddie Murphy

as Rodan in SimonVerse: The Series

Seth Rogan

as Anguirus in SimonVerse: The Series

Steven Yeun

as Noah in SimonVerse: The Series

Lana Condor

as Ruby Gillman in SimonVerse: The Series

Denis Leary

as Earl in SimonVerse: The Series

Jack Black

as Simon in SimonVerse: The Series

Ben Kingsley

as Kratos in Simon x Ruby: Dawn of the Kaijus

Lacey Chabert

as Shimo in Simon x Ruby: Dawn of the Kaijus

John Oliver

as Baragon in Simon x Ruby: Dawn of the Kaijus

Gary Anthony Williams

as Dagon in Simon x Ruby: Dawn of the Kaijus

Mandy Moore

as Scylla in Simon x Ruby: Dawn of the Kaijus

Dodo (ARK: Survival Evolved)

as Chunky in Simon x Ruby: Dawn of the Kaijus

Toni Collette

as Agatha Gillman in Simon x Ruby: Dawn of the Kaijus

Ray Romano

as Behemoth in Simon x Ruby: Dawn of the Kaijus

Common

as Methuselah in Simon x Ruby: Dawn of the Kaijus

Patrick Warburton

as Gorosaurus in Simon x Ruby: Dawn of the Kaijus

Doug (MonsterVerse)

as Doug in Simon x Ruby: Dawn of the Kaijus

Brambleboar

as Brambleboars in Simon x Ruby: Dawn of the Kaijus