Suggestions by @cartoonmultiverse

Lord Shen

as Lord Shen in Aang

Kang the Conqueror (Marvel Cinematic Universe)

as Kang the Conqueror in Aang

Catra

as Catra in Aang

He Who Remains (Marvel Cinematic Universe)

as He Who Remains in Aang

Twilight Sparkle

as Twilight Sparkle in Aang

Wolverine (Marvel Cinematic Universe)

as Logan/Wolverine in Aang

Iron Man (Marvel Cinematic Universe)

as Tony Stark/Iron Man in Aang

Miss Martian

as Megan Morse/Miss Martian in Aang

Zuko

as Zuko in Aang

Aang

as Aang in Aang

Raphael (TMNT 2007)

as Raph (07) in Aang

Donatello (Rise of the TMNT)

as Donnie (Rise) in Aang

Donatello (TMNT: Mutant Mayhem)

as Donnie (MM) in Aang

Leonardo (Rise of the TMNT)

as Leo (Rise) in Aang

Leonardo (TMNT 2003)

as Leo (03) in Aang

Leonardo (TMNT 2007)

as Leo (07) in Aang

Doctor Strange (Marvel Cinematic Universe)

as Doctor Strange in Aang

Invincible (Mark Grayson)

as Mark Grayson/Invincible in Aang

Vox (Hazbin Hotel)

as Vox in Aang

Boris and Doris (Caillou)

as Doris and Boris Anderson in Aang