X-Men vs. Street Fighter (known as XSF to Street Fighter fans) is an arcade game released by Capcom in 1996 and is the first game in the Marvel vs. Capcom series of fighting games. It features characters from the X-Men franchise and characters from the Street Fighter game series. It was the first game to blend a tag team style of combat with the well-known Street Fighter gameplay, as well as incorporating elements from Capcom's previous fighting games in the Marvel Comics franchise, X-Men: Children of the Atom and Marvel Super Heroes.

It was also ported to the Sega Saturn in 1997 and PlayStation in 1998. However, the tag team system was omitted from the PlayStation version due to memory limitations. Due to insufficient beta testing, every character in this game has at least one infinite combo; ironically, it is nevertheless praised by some Street Fighter fans as being the most "fun" entry of the four Marvel vs. Capcom games for precisely this reason.

X-Men vs. Street Fighter uses a system similar to the style developed in Marvel Super Heroes, and adds the tag team gameplay feature. Instead of picking one character, a player picks two. The starting character can then tag the waiting one in at any time by hitting the Fierce and Roundhouse buttons, which activates the "Variable Attack"; the incoming player will jump in with an attack and taunt briefly. During their taunt, they are vulnerable to counter attack. (Wikipedia)

Codes

Hidden EX Option Mode
At the main menu press Triangle, Triangle, Right, Circle, L1 - Hidden EX Option Mode

Unlockables

Misc. Unlockables
Akuma - Highlight any character in the top row and press Up

Alpha Chun Li - Highlight Chun Li and hold Select for five seconds, then press X

Apocalypse - Highlight Akuma, hold Select for five seconds and press R1

Hyper Chun Li - Highlight Chun Li, hold Select and press R1

Secrets

Attack Opponent After Winning a Match
After you win a match and your character does his/her victory pose, press Start. You'll be able to attack your fallen opponent while he/she is down.

Original Costume Colors
When selecting a character, press LP or LK

Great fighting game in its days: