Graphics for Super Mario World hacks
ROM hacking (Super Mario World to be exact) has been a major influence on my creative skills and output.
Drawing graphics for Super Mario World was my first foray into pixel art (or any digital art, for that matter). I've since drawn a handful of custom graphics for the game — foregrounds and backgrounds as well as fonts — and uploaded them to SMW Central for others to use. (The submission dates on the site aren't always accurate since many of them were reuploaded years after they were made.)
I'm listing these here for the sake of completeness, but most of them are seriously outdated. The graphics I draw nowadays I don't submit to the site but use in A Plumber For All Seasons, so that better represents my current skills.