In 2007, I started messing around with hack tools that I had discovered a few years
before on zophar.net.
The first and best so far of these creations, though full of bugs and never fixed, was Super Mario Bros: Jerry's Remix. The color
schemes were one thing that I messed with by altering environment settings that didn't originally mix with other settings.
For example, my scenery was a toadstool level in one of the worlds yet it was underwater with all the above-water enemies. So all of the toadstools became pink and green.
I had also began to edit the US sequel to the game. However, only one level worked after retrying again and again with Super Mario 2 Discombobulator.
On the contrary, Super Mario 3 From Hell (only one world was finished) and a few other SMB3 hacks were able to be started. I just eventually lost interest and finished with Super Mario Bros: Jerry's Remix 2 which also had never seen a finished form.
Someday I hope to not only rehash my past hobby of hacking Super Mario Bros games to include different levels, but also experiment further with new tools I have found on romhacking.net.
I'd like to manipulate many other NES games of this era to be graphically different or have a full set of new levels to play. My next target would probably be something like Bubble Bobble, a game that has over one hundred levels.
If you want an easier way to make your own levels, try: Super Mario Bros X
...or just buy Mario Maker for Wii-U if you have one.