In regards to the Prisoner's Dillema, check out superrationality. It may be practical in a thread about a "perfect game."
Some games can be played perfectly with a loss. Michael mentioned Connect 4. The second player can play perfectly, which here means survive as long as possible. If he lost within the first four moves, well, he's retarded.
If Super Smash Bros. is comparable to Connect 4, then -- and for simplicity let's imagine only 2 players -- the loser will survive as long as possible, take as little damage as possible, lose as few lives as possible, etc etc etc. This all depends on the criteria you decide is important for "winning" without a technical win in Super Smash Bros.
Some games will never have a winner, but would be a stalemate. Those would be pretty shitty games in terms of theoretics. I just invented one in my head right now. Imagine a game where there are two players. One can move three spaces on an infinite grid, and the other can move only one. If the only way the game ends is for the slower piece to capture the faster one, then only a retard would ever lose as the faster piece. The game, from a theoretical perspective, is stale.
Now we're the retards in Super Smash Bros. The reason why the games are fun are because of our imperfections. Given such a vast amount of possibilities and decisions to make, we rely on quick wit and heuristics to read and predict the game.
For some reason, I'm imagining that a perfect game of SSB would just be players standing idle, incurring no damage. Or, maybe they could evade each other so well, no one would ever get hit. This is like the theoretical game I made up earlier, except on a finite plane. Given 4 characters, though, and limited level space, I'm not sure evasion would be possible.
We could use multi-variable graphs for all of the characters. We plot what we consider is important: speed, weight, power, jumping distance (to keep from falling in a pit.) The one with the most area would be the best player. This would be a bitch and a half to calculate though. Also, item drops may give a technically weaker opponent the advantage.
Gah, my brain just broke. Good luck.