Over the weekend I decided I wanted to make Super Mario Bros. in Minecraft.
Here are screenshots of my progress. (the only mod I have used is an Inventory Editor)
Here is the start of World 1-1. The map is 3 blocks wide.
This is how I made the boxes that drop stuff
I used dispensers and placed them in the background with pressure pads on the ground where they would be.
Here is the underground part where you collect coins.
I had to put a nether portal at the end and a pipe in the nether with another portal at the end that goes back.
This is because the distance between where the pipe goes down and comes back up is about 90 blocks so I decided to shorten the gap using the nether.
And here is the end of World 1-1 and the start of 1-2.
The pipe will go underground and I will continue there.
I think this is good game design practice.
(click the images to view higher res)
Edit: The next update will probably come out when I have completed 1-2. No guarantee when that will be.