Brutal Mario
Brutal Mario is an SMW Romhack first released on SMW Central in 2008 that is filled to the brim with custom graphics, bosses, gimmicks, and such taken from other games. It is one of the most praised rom hacks back then, though recently it's seen a lot of backlash for uninspired level design and it's boss battles being patience trying. Even still, it is a technical marvel of it's time that has since inspired many novices to join SMW Hacking communities and create some of the most memorable hacks of today's age. Ever since it's initial Demo 7 release, the author carol has released demos up until 2012 featuring bosses that completely change up the game of Super Mario World achieved by improved HDMA and Mode 7, special mentions going to the bosses Dark Lich, Bow, 7 Heroes, and even a Star Fox-like shooter battling one of the airships from Chrono Trigger. A few of those demos also contained new overworlds and submaps that were very ambitious for it's time.
The popularity of Brutal Mario has also led to some fake demos, screenshots, and videos claiming to be the next big thing the game has created. Someone even hacked into carol's account on Super Mario World Central to provide a convincing amount of screenshots, later debunked by members to the community with the real user admitting to his prank later on. Ever since, the game hasn't gotten any news, with the latest demo still being from 2012.
Maybe some day, Brutal Mario will return. But for now, it'll always be known for it's revolutionary ambition to create the only known successful crossover romhack around.