We had a thread about multiplayer earlier... I'll go see if i can find it for you guys.
EDIT: Here was my original idea
I always just thought of simple split screen for local mp would be kinda fun. It'd just be a race to see who could beat each level first, and when somebody completed the next level would load then they could go!
You could even put some custom maps in
so here is what I envision:
-Dude 1 Hosts a Multiplayer Race Game
-Dudes 2 and 3 join the game. They are all Meat Boys of different shades, or you could just put a colored arrow above each player ALA SSBB(but you can also select other characters you have unlocked)
-They race in a level. Dude 2 dies halfway through and respawns for another try. Unlimited Lives
-Dude 1 barely beats Dude 3 at the end, and Dude 3 chooses to switch to Jill for the next level.
-Dude 1 gets +10 points for beating a level, and Dude 3 +5.
-The next level loads, Dude 3 wins this time. Dude 3 gets +10 and Dude 2 coming in second place gets +5
This will continue until they play 10 races or so.
A neat idea, but with things like the keys and disappearing blocks, that could wind up annoying (though I suppose it could work on different screens as I'm sure you've invisioned).
To get a decent idea of this, go play Jumper Redux, it has a multiplayer almost dead on with this (Spoiler alert: Meat Boy is based on the Jumper series). Players connected over a LAN connection (yay Hamachi) and did basically this.