Why Couldn't the PlayStation Marvel vs. Capcom Do Tag Teams?
In the arcade, Marvel vs. Capcom is a tag team game: each player picks two fighters and can swap between them at any point, so a match needs four complete characters loaded at the same time, each with hundreds of hand drawn animation frames, plus a randomly assigned Special Partner waiting to be summoned.
The PlayStation could not do that. Capcom said so at the time in effect, reviewers documented the result in detail, and the port that shipped in 1999 and 2000 is built entirely around the workaround. Here is the arithmetic.
THE TWO COVERS
Same game, two shelves

THE MEMORY PROBLEM
Documented, piece by pieceTHE CONTRAST THAT PROVES IT
Same game, more memory, no cutsThe Dreamcast version of the same game, released months earlier in 1999, keeps full tag team play and was praised as a flawless, arcade perfect translation. Nothing about the game design changed between the ports. The hardware budget did, and the feature list followed it exactly.
Reviewers noticed immediately. GameSpot scored the PlayStation version 5.8 out of 10 against 9 out of 10 for the Dreamcast version, and Jeff Gerstmann’s verdict has become the standard summary of the port: it has the same moves as the original game, but the shell surrounding those moves is completely different. GamePro took the other side of the same fact, praising Capcom for cutting features rather than overloading the system. Both reviews agree on the cause: memory.