Metatron (Supernatural)

Morgoth

Molag Bal

Mehrunes Dagon

Morbius

Molecule Man

Molten Man

Mephisto

Mister Freeze

Malthus (The Conjuring Universe)

Michael Myers

Michael (Supernatural)

Michael (Apocalypse World, Supernatural)

Moloch (Sleepy Hollow)

Moloch (Supernatural)

Mercer Frey

Morgan Elsbeth

Mother Talzin

M.O.D.O.K.

Maul

Mitth'raw'nuruodo (Grand Admiral Thrawn)

Mangog (Marvel)

Morgan Le Fay (Marvel)

Morgan Le Fay (Arthurian, depending on version)

Morgana (The Kid Who Would Be King)

Magneto (Sometimes)

Mastermind

Master Mold

Martin Brenner

Mr. Mercer (Pirates of the Caribbean)

Malacath

Moonstone/Meteor

Marik Ishtar (Yu-Gi-Oh)

Mizar (Yu-Gi-Oh Zexal)

Mr. Heartland (Yu-Gi-Oh Zexal)

Mind Flayer (Stranger Things)

Madame Hydra

Madame Masque

Madame Hel

(The) Mandarin (Marvel)

Maven Black-Briar (Skyrim)

Mystique (Marvel)

Mance Rayder (Game of Thrones)

Mixmaster

Moff Gideon

Meltdown (Transformers)

Moralo Eval (Star Wars)

Malice (Marvel)

Movarth (Skyrim)

Merrin (Star Wars)

Marrok (Star Wars)

Medusa (Percy Jackson)

Moloch (Darksiders)

Megan Parker from Drake & Josh

Mr. Dawes, Sr. from Mary Poppins (1964)

Mr. Perkins from Despicable Me

Millicent Clyde from Paddington

Marvel from The Hunger Games

Ming-Hua from The Legend of Korra

Makunga from Madagascar: Escape 2 Africa

Man Ray from SpongeBob SquarePants

Master Udon from SpongeBob SquarePants

Maleficent from Sleeping Beauty

Mother Gothel from Tangled

Madame Rouge from Teen Titans

Master Org from Power Rangers Wild Force

Mesogog from Power Rangers Dino Thunder

Master Xandred from Power Rangers Samurai and Power Rangers Super Samurai

Madame Odius from Power Rangers Ninja Steel and Power Rangers Super Ninja Steel

Magneto