Mother 4 - The Fan Game http://mother4.andonuts.net/
(Dave goofed when putting together the first one. This one is corrected; the audio now lines up correctly.)
One of the most notable things about the Mother series has always been its music, and having the SNOBODYS on board has really been a blessing, making sure one of the most delicate features of the project is right where it needs to be. Stitch and Zephys were having a conversation about how each character in Mother 3 had their own "instrument" for when they attacked, and how it really put some more soul into the game. After toying with this idea a little bit, we came up with the idea to expand on this, and this is one of the results.
Rather than having a single level-up jingle, each character has their own. When multiple characters level up at the same time, their jingles play simultaneously, creating a more complete song. It really makes those experience cash-cow boss battles all the more satisfying to level off of, since you're hearing the complete level-up symphony. Here it is in action, complete with a few combinations of jingles.
In execution, it's a really minor improvement that makes a world of difference when it comes to experiencing the game.