@minishcapper: Unfortunately it wasn't either of these; it was pretty pixelated and had a more basic color palette, which is why I'm thinking along the lines of GB Classic. I also don't remember there...

I found a Gameboy game sometime between 2002 - 2008 at an old GameCrazy. I played it on my GBA, but I don't recall it being in color, and I seem to remember it being the size of a larger gameboy cartr...