Billy got an early copy of Super Mario World today. So the big question is, will it connect will Super Mario Advance 1 for multi-cart multiplayer? The final answer inside.
The link for multi cartridge Mario Brothers works just fine between Super Mario Advance and Super Mario World.
You can play both Classic and Battle versions of Mario Bros. just fine. When both games start up, select Multiplayer on Both GBAs, and the systems look for each other...and link up.