Using the Pro Action Replay code 7E1F032B for the level modifier, you can access a small debug area. It starts out exactly the same as stage one, but when you get to the first stop, there will be barrels. Each barrel will have a different object in it. Once the items cycle, each of the regular enemies in the game will appear, but one hit will defeat each of them.
Once you defeat the enemies, you're pretty much stuck there. Kinda neat to try out though.
(Code by: Aether Knight)