A while ago as practice for fun I had a go at recreating mario in Flash, the physics still arn't perfect, but I think I got them pretty close. Was fun programming an old classic. This is a good way to practice making platformers smooth and seeing how mario did it. Play and/or download the engine below.
Click below to play the engine. Arrow keys to move.
Click below to download the flash file.
It's in Actionscript 2.