Bahamut vs. Mewsan

A scene from a supposed deviantART-based version of "Subspace Emissary".

Bahamut sees his Gummi Ship Vena (which was stolen before) engaged in air combat with the Gummi Ship Cosmi (Lava's battleship-class Gummi Ship) above a tall mesa with a haunted mansion on top of it. Angered at the flagrant misuse of the Vena, Bahamut left Leo, Sui, Yoshiken, Anjil, and Katie Tiedrich to reclaim it.

He flew up the mesa and reached the top, where he was just very near to the mansion. He also noticed a frilly young magician named Toni Tafoni about to enter the mansion, from which she supposedly got a party invitation. However, the moment she opened the door, a plethora of ghostly Subspace monsters come after her. Fortunately, Bahamut jumped in and fought back against these ghouls. However, they started overpowering him. That's when Tafoni hurled a special playing card at the monsters, inflicting onto them a gigantic explosion, destroying them. After Bahamut told her his situation, Tafoni decided to help him out.

After many mind-bending rooms and battles, Bahamut and Toni Tafoni make it onto the rooftop of the mansion. Tafoni looked side-to-side, but couldn't see the Vena or the Cosmi anywhere in the sky. Bahamut, however, had his attention caught on something else. He saw one of the tall, pointed rooftops, with a white/purple figure atop it, standing on the roof on the tip of one foot, in some sort of meditative stance. This figure is Mewsan, an extremely powerful Psychic Pokémon.

Mewsan's third eye, on his forehead, immediately opened up upon detecting Bahamut's presence. Then, his other eyes flashed open. He turned his head towards Bahamut, then jumped from the pointed roof to the flat roof that Bahamut and Tafoni stood on, much to the two's surprise. Mewsan held his hand out at Bahamut as it radiated with psychic energy, as if to challenge him. Bahamut nodded slightly, then motioned for Tafoni to stand back. Tafoni, needless to say, wasn't very comfortable with this situation, but stood out of it anyway. And so, Bahamut and Mewsan faced off with each other.

Bahamut (c) UMS Productions
Mewsan (c) Myuutsufan

These aren't shown, but they're mentioned, so...

Leo Winters (c) Leoshi
Sui (c) YamiAmey
Yoshiken (c) himself
Anjil (c) herself
Katie Tiedrich (c) Hail-NekoYasha
Toni Tafoni (c) BlackLillian