Capcom vs. SNK Millennium Fight 2000

Capcom vs. SNK: Millennium Fight 2000 is the second entry in the SNK vs. Capcom series, part as well of the Capcom vs. Whatever series. It was developed by Capcom and released in 2000 for arcades and the Sega Dreamcast.

This game was notorious for containing almost only Street Fighter and KOF characters:

Capcom side:

From Street Fighter: Ryu, Ken, Sagat.
From Street Fighter II: Chun-Li, Zangief, E. Honda, Guile, Blanka, Dhalsim, Balrog, Vega, M. Bison, Cammy and Akuma.
From Street Fighter Alpha: Sakura and Evil Ryu.
From Darkstalkers: Morrigan.

SNK side:

From The King of Fighters: Benimaru Nikaido, Kyo, Vice, Rugal Bernstein and Iori. (Plus his Orochi Evil Counterpart)
From Fatal Fury: Mai, Terry, Raiden, Kim Kaphwan, Ryuji Yamazaki, and Geese Howard.
From Art of Fighting: Ryo, King, and Yuri.
From Samurai Shodown: Nakoruru.

The gameplay featured the use of the Ratio, which gave all the characters a specific rating from 1 to 4, thus determining the amount of places in the team (whose ratio shouldn't be more of 4 as of the combined team) said character would occupy. The game also contained two grooves: SNK's The King of Fighters ‍'‍94-‍'‍98 groove, and Capcom's Street Fighter Alpha one.

An Updated Rerelease of this game would follow, called Capcom vs. SNK: Millennium Fight 2000 Pro would contain ALL these characters unlocked from the start, plus the inclusion of Dan Hibiki and Joe Higashi.

Tropes used in Capcom vs. SNK Millennium Fight 2000 include:

Ambidextrous Sprite: Sagat's eyepatch.
Art Shift: Reuse of Street Fighter Alpha sprites, and the ensuing clash in art style and animation quality, was one of the strongest complaints about the game. Morrigan's constant reuse of her very first sprite is still a vivid running joke in many circles.
Assist Character: Morrigan is assisted by Lilith.
Big Bad: Geese and Bison.
A Boy and His X: Nakoruru and her hawk Mamahaha.
The Cameo: Hon-Fu makes a cameo in the intro to Chun-Li vs. Yamazaki matches.
Comeback Mechanic: In the Millennium Fight 2000 series, the most obvious examples are S-Groove (where an opponent gains infinite meter while close to death) and K-Groove (attacks do more damage and they receive access to a Super Move) but only lasts a limited amount of time and ends the moment the Super Move is used.
Damn You, Muscle Memory!: The game used a four-button layout, leaving Capcom vets with a whole new world to learn.
Department of Redundancy Department: "Millennium Fight 2000". We can probably figure the right millennium for ourselves.
Dialogue Tree: The games are full of this, with stuff like Geese throwing a Reppuuken at Bison to blow his cape away.
Everything's Better with Spinning: Zangief.
Gainaxing: Mai (obviously).
Panty Shot: Sakura, thanks to the magic of recycled Alpha sprites.
Shout-Out: Check the page.
Stripperific: Morrigan, who's technically not even wearing clothes!
Surprisingly Good English: Cammy had an English voice actress.
The Unexpected: In-universe; when you beat the game (at least before the rerelease) the ending cutscene shows that Dan Hibiki and Joe Higashi won the tournament while you were off beating the final boss.
Updated Rerelease: Capcom vs. SNK Pro, which was basically Capcom vs. SNK with all the unlockables available from the start and the addition of Joe Higashi and Dan Hibiki to the roster.