ok I've been working on a mario engine I'll release open source.
here is a list of current features, if you can think of any more then please let me know:
springs
variable jumping
goombas
koopas
koopa shells
big mario
? blocks
starman
parallax BGs
BGM
note blocks
moving platforms ( for some reason you can't move left or right on a platform that goes down)
coin blocks
Features on the way:
fire mario

link: http://www.sendspace.com/file/kub8g9

actually, theres a way to do that. Theres a tutorial i had found before that was moving platforms from left to right, and up and down, and you can move and jump off the platforms. ill try to find it. If i can think, i think icuurd made it.

EDIT
K. i tried out the game, and its pretty good.

Sugesstions:


Make a global variable for mario's state, like in a controller that is only used once for mario's state: global.mario = 1 (meaning thats small mario) or use global.mario = 'Small Mario' (i think this would be much easier) Use the states as follow, if ya want to:
'Small Mario', 'Big Mario', 'Fire Mario', 'Cape Mario', 'Raccoon Mario', 'Hammer Mario', 'Tanookie Mario' (dont know if i spelled that right, but this one is like Raccoon Mario, just it transform into a Statue)

? Blocks

When you hit the blocks (an item in this case), make mario states, and then when it hits, it will check to see if the states are what it is. Say like you made a Fire Block. Once you hit it, and you are 'Small Mario' state, it will instead turn into a mushroom. If you are not, then it turns into a flower.
Platforms

Maybe this can help you in doing the moving platforms. It's very smooth to use, and you can move and jump while its moving: http://host-a.net/icuurd12b42/movingplatformsallout.gmk

For the starman, its good that you have that working. make some animated stars, and let it follow mario, until it ends. Also the star bounces too high when it hits the ground, or any other objects. Set to a steady vertical speed that it'll used when it hits the ground or an object.

I was going to turn the game from D&D to GML, just haven't gotten around to it yet :P
as for the different types of mario, I'm only planning on having small,bi and fire mario.
I haven't gotten around to fire mario yet so i haven't made the variable global.

Here is a small way of turning into Small, Big, Fire Mario by goin into different rooms. This is only one room of course, but it work just like goin into different rooms. The title screen has the global set for moario's state, starting off as small mario first. The item box has been set to red as represent as fire block. The sprite_index will change it into the block as it suppose to be. Try it.

PS: I dont know if you have GM8, cause this is in 8. Ill transfer it to GM7, or GM6 for ya.

Super Mario Bros 2.gmk