Stage Builder
Super Smash Bros. Brawl will allow you to create custom stages. First, you select the size of the stage, which can be small, medium, or large. Then, you pick one of a couple of pre-made backgrounds and a music piece to play on it. The music can come from the game, or from your SD card. Then, you set the terrain. There are different structures and building materials you can use depending on the background you chose earlier. you are limited in the number of parts you can use per stage. Once you are ready, you can test the stage through the editor, than switch back to the editing screen if you want to make any more changes. You can send one stage per day to Nintendo. In addition, Nintendo will offer a "stage of the day" that you can battle on for one day only. You can also send stages to your friends, and they are compatible with SD cards. You can only have as many custom stages as however much room you have in your internal Wii memory and SD card.
Types of parts you can use in this mode range from standard pieces, like blocks and ramps and stairs, to structures, like trees and mushrooms and rock arches, to features, like the Drop Blocks, which begin falling if stepped on long enough. Drop Blocks eventually respawn, and can only be activated from above, making it possible to make one-way doors of a sort.
In addition, you'll see that this mode comes packed with interactive terrain objects. For example, you'll find that you can make platforms that will move, up or down, or possibly, side-to-side. This will create many options for map makers. There are also "traps," like spikes for example, that can be implemented into the map. Ultimately, in this mode you are limited by your own level of creativity. Many people have even resurrected some super smash bros. 64 stages.
Unlockable Parts
You can actually get more parts to add to your stages! Here is the different parts and how to get them:
Edit Parts A:play 10 times or more on stages you made.
Edit Parts B:create 5 or more stages in stage builder.
Edit Parts C:create 15 or more stages in stage builder.
