A Mini-Boss is a type of boss in the Metroid series which, while still posing a challenge, is smaller and/or weaker than a regular boss in the respective game. Defeating a Mini-Boss is sometimes necessary to accomplish a larger goal or reach an item.
Some Mini-Bosses are stronger versions of regular enemies, such as the Plated Beetle, Sheegoth, and Cloaked Drone, and may appear later in the game as normal enemies. In these cases, the Mini-Bosses have a special music theme, such as VS. Giant Beetle, during their first encounter that is not shared with normal enemy encounters.
When not officially designated as such, it is not always clear where the distinction lies between stronger enemies and Mini-Bosses, or Mini-Bosses and weaker bosses; this distinction may be up to the player's discretion. Therefore, this article only lists enemies and bosses that are directly referred to as Mini-Bosses in official Metroid media.
List of official Mini-Bosses[]
Metroid[]
In the manual, Kraid and Ridley were called "Mini-Bosses" as their defeat was necessary to access the final boss, Mother Brain. For their appearances in later games, they were considered regular bosses since hardware improvements led to an increase in their size and power.
Super Metroid[]
In the manual, the Spore Spawn and Crocomire are officially designated as the Mini-Bosses of Brinstar and Norfair, respectively. Spore Spawn's battle music is titled Mini Boss Confrontation BGM in Super Metroid: Sound in Action and is shared with Botwoon, which is also referred to as a mini-boss by Super Metroid Nintendo Player's Guide.
Metroid Prime[]
These bosses are designated as Mini-Bosses by Metroid Prime Official Perfect Guide.
Metroid: Zero Mission[]
Although this game contains several weaker bosses (such as Charge Beam Beast and Acid Worm), the Imago is the only one officially referred to as a miniboss by Metroid: Zero Mission: The Official Nintendo Player's Guide.
Metroid: Other M[]
These enemies are classified as Mini-Bosses by Metroid: Other M Premiere Edition.
Metroid Dread[]
The internal music files designate these enemies' boss battle themes as "Boss Mid", indicating that these are officially considered Mini-Bosses.