The following is a list of all the enemies encountered in Metroid: Zero Mission by region.
Deorem
Dessgeega
Geemer
Hive
Mellow
Parasite
Ripper
Skree
Tangle Vine Fruit
Waver
Zeb
Zoomer
Atomic
Black Zebesian
Mecha Ridley
Ruins Test
Red Zebesian
Zeela
Skultera
Acid Worm
Baristute
Gadora
Geega
Kraid
Reo
Sidehopper
Dragon
Gamet (purple)
Gamet (red)
Geruta (red)
Geruta (green)
Kiru Giru
Mella
Multiviola
Polyp
Ripper II
Sova (purple)
Sova (red)
Squeept
Tangle Vine
Holtz
Imago
Ridley
Viola
Zebbo
Turret
Metroid
Mother Brain
Rinka (red)
Rinka (green)
Zebetite