Any platform object can be either solid or a "cloud," and can move.
Level editors are a must in a game like this. Without one, you will spend too much time hand-typing XML files.
This game is coded in a very OO way. This allows for the game to be easily extensible (meaning that you can add features without much trouble).
The background image moves independently of the foreground (the overlay movie-clip instance). The hero is contained within the overlay instance.
We use an iterative-stepping technique to work around Flash's snapshot frame-dependent collision-detection nature. Using this technique, we look at where the hero was in the last frame and where he is now, and then divide this distance into steps.
This game can be easily enhanced with any number of creative features.