METROID MUTANT
Alongside the games, the Metroid series has had a long history of comics and other media running alongside them, some even supplying details that made it into canon. One of the strangest of the earliest media was Metroid: Zebes Invasion Order, a “gamebook” that acted as a sort of playable choose-your-own-adventure computer game, that ran you through the plot of the first game, but in text form. This game included a bonus ending that had you going up against a secret boss.
This was the Metroid=Mutant, but I’m calling it the Metroid Mutant. The Metroid Mutant was a mutated Metroid that survived the defeat of Mother Brain, and, depending on your choices, followed Samus onto her ship as she escaped the planet's destruction.
As a fighter, the Metroid Mutant is big and powerful, with attacks based on what it was portrayed to do within the gamebook, with maybe a little creativity on the game maker’s part to portray the moves visually.
Likelihood rating: Non-game (technically).
