MGS4 Bosses/characters vs MGS1 bosses/characters
Some spoilers of characters from MGS4, so don't check if you don't want some secrets about them spoiled.
The renegade Foxhound and the two intruders of Shadow moses face off against the B&B unit and their superiors. (Plus Old Snake and Raiden)
You simply state who wins in the matches that are already put in there, then if you feel like it, you can match the survivors against each other to see which team prevails.
MGS1: Gray Fox vs Raiden : MGS4
Solid Snake vs Old Snake.
Liquid Snake vs Liquid Ocelot. (Unarmed, since we don't see anything else from LO.)
Vulcan Raven vs Raging Raven.
Ocelot vs Laughing Octopus.
Sniper Wolf vs Crying Wolf.
Psycho Mantis vs Screaming Mantis.
Since Decoy Octopus is basically worthless, I'll just put Gray Fox back again...
Gray Fox vs Vamp. (One with Vamp as he normally is, and one when his nanomachines are suppressed.
Every fight is where you fight the characters in MGS1. So Gray Fox matches = Hal's Laboratory, etc.