Version 6.0 is infamous for its "Hardcore" stages. These levels predate the mainstream popularity of Kaizo Mario (brutally difficult romhacks) for many casual PC users. The design in these stages shifts from "exploration" to "execution." Player are required to memorize patterns, utilize glitch mechanics inherent to the engine, and perform mid-air adjustments that require clairvoyant foresight.
To access World 9, you must complete all eight worlds without using any warp zone or secret exit that skips worlds. World 9 is notorious for its extreme difficulty—challenging even veteran Super Mario Bros. players. mario forever 6.0