The perfect ending
I was not that a big fan of the "Mario Brothers" series, but this cemented my place as a fan of yours. Apart from having great graphics (these are some of the lowest Mario graphics, but done so well) it had one of the best endings ever. While everyone dying might seem kind of morbid, it truly shows a philosophical aspect. Is this all that Mario is doomed to do and that we are doomed to do in these scenarios? Will nothing but vengeance and want for total destruction lead to our own demises? How nice of how to make this perfect conclusion only for Newgrounds.