Meryl

Full name Meryl Silverburgh. Dressed in cosplay as Rogue (Anna Marie)

EVA

Dressed in cosplay as Emma Frost

Mantis

Psycho Mantis Dressed in cosplay as Legion, so he's not wearing his gas mask.

Miller

Kazuhira Miller, dressed in cosplay as Cyclops (Scott Summers) with a leather X-Men jacket and red shades

Raiden

Raiden (Jack) is dressed as Angel / Archangel

Snake

Solid Snake (Iroquois Pliskin or David) is dressed up in cosplay as Gambit. He did it mostly because Meryl asked him to and so many others were going to be at the party. He's just happy to have the chance to see friends again in a non violent context. But he's still himself about it.

Otacon

Hal Emmerich also known as Otacon is dressed in cosplay as Beast (Hank McCoy)

The Boss

The Boss or The Joy is here dressed as a comic accurate look for the character Mystique, painted fully blue with glowing yellow contact lenses. There was an alternate concept featuring her as Storm but it wasn't gone with ultimately.

Naked Snake

John also known later as Big Boss is dressed in cosplay as Wolverine smoking a cigar and wearing a leather jacket.