From the Super Mario Wiki, the Mario encyclopedia
Special 8-Crown is the final level of Special 8 and is the 96th and final level in Super Mario 3D Land. It contains no Star Medals. It is only unlocked after obtaining 5 stars on the save file, and is designed to be the most difficult level in the game, similar to The Perfect Run, Champion's Road, and Darker Side.
The player starts off on a platform next to some Toads, Hammer Bros., and Boomerang Bros. At the end of the platforms is a Warp Box that leads to an area that contains several platforms along with some Goombas and several other enemies. At the end of this section is a Warp Pipe that leads to a boss fight with Boom Boom and Pom Pom (with Pom Pom's boss theme used). After the player defeats them, a Warp Pipe appears.
In the next area is a Switchboard that goes past some Fuzzies, some Tail Bob-ombs, and some Fire Bars before leading to a Warp Box. In the next area are several Donut Lifts and Fire Bars with a Warp Box at the end. In the next segment is a Big Cosmic Clone, some Burners, and some Chain Chomps with two Wallops guarding the Warp Box.