The Mctwist is a type of 540. This trick is typically done on vert ramps but can be done in pools as well. Dalton Dern can do this trick on any ramp imaginable, including 4ft tall mini ramps. Yes, you read that correctly. He is unbelievable and the rules of physics do not apply to him.
The Mctwist is different from a flat spin 540 because the skater actually goes inverted during the twist. The proper grab for the this trick is a mute grab. Some skaters recommend learning how to do frontflips with a full twist on a trampoline before taking it to the vert ramp.