You can remix this boss add attacks, phases, new songs, new gimmicks. Just don't have you're super strong OC overtake the boss and become it's whole own thing. That's lame. You can update the bosses sprite if you'd like, but I'd prefer if it was recognizable as the same boss from the start. Bassically, don't replace the entire project. After the boss is pretty cool, I'll make a video fighting it and give credit to everyone who remixed in the description.
@Jomamajojo for the original I added three attacks (some of them I also plan to use for future bosses)