Super Mario All-Stars Randomizer:
Game loads up to a start screen menu where you select the number of levels to be played (probably using the menu system already built into the game menu. Select number of levels to be played increments of 10 or something. This could possibly be done in the randomization app instead of in game for race simplicity).
Levels are pulled from all games. You can weight each game in the app to change the rate at which each game is represented.
SMB2USA will choose random characters for each level that shows up.
Not sure how persistent power-ups or number of lives should be handled (You play a smb3 level and finish it with racoon mario, the next three levels are from other games before another smb3 level pops up. Do you still have raccoon mario? If so, does dying in a smb1 level cause you to lose that persistant powerup the next time you come across a smb3 level?)
Basic cosmetic functionality like sprite swaps, palette swaps, bgm/sfx randomization, MSU_1 support, etc.
Basic functionality of randomizers that are already in place so that each game may also have it's enemies and powerups shuffled.