A Metroid Crossover

A meteor, resistant to magical manipulation, crashes in Equestria, Planet Equis, and soon spreads an unknown poison throughout the land. Containment is all but failing and the Princesses have little power to stop the spread of the Great Poison. The Elements of Harmony are of little use as no knowledge exists of this threat that consumes all life. Help comes from a certain Hunter, clad in metal.

Samus Aran will not only fight for her life as always, but her own sanity as well as these ponies that she begrudgingly starts seeing as allies. New horrors and abilities await her as a reason to fight slowly festers within her, possibly unlocking something she had been denied for so long: Friendship.

Notes and Resources:

This takes place after Echoes. The events of Corruption will have not happened yet. In terms of MLP, consider everything up to and including the Crystal Empire. Princess Twilight does not exist here, etc. The official Metroid Timeline can be found here.

As well, this story references the manga in many places. Reading of it is not required and I try my best to explain the context, but if you're interested, both volumes can be found here.

EDIT: This story was written over two and a half years, beginning in 2013. You'll probably notice the difference in writing as the chapters progress.

This story is a sequel to Metroid Equis

With the culmination of events on the BSL Research Station, Samus Aran is finally able to come back to Equestria, Planet Equis; to come back home. Much has changed in her absence, but it is still the friendly, peaceful, welcoming planet and nation that she left behind two and a half years prior. With the Space Pirate threat neutralized and the secret, illegal Metroid militarization programs destroyed, it appears that Samus can finally take another massive breather with her friends and enjoy some well-deserved rest, recovery, and relaxation. The galaxy is finally at peace.

At least... for a short while.

A new enemy, one much closer to home, soon rears its head, threatening all of Equestria and Equis with complete and utter annihilation. Their mission: revenge. Samus will fight with all of her being alongside her allies against an enemy who would like nothing more than to see all that she holds dear, including her home planet, completely razed. In so doing, her cunning, ever determined enemies unleash a weapon so unexpected, so eerily familiar yet horrifically foreign that even Samus herself just might prefer the late Ridley or the SA-X...

Editing Team: Random_Dragon; ToxiClay

The Metroid Timeline/Chronology (confirmed by Nintendo) can be found here.

Canon Considerations
MLP-FiM: Up to AND including "Magical Mystery Cure." (Seasons 1, 2, and 3)
Metroid Series: Everything up to AND including Metroid Fusion (Including original mangas. See official timeline above). So, effectively everything.