The Flop Block
The Flop Block is a glitch in Super Smash Bros. Brawl. It works roughly by activating a drop block, walking up a slope, and back to where the drop block would be, at which point the player teleports on top of the falling drop block, often going past the lower blast line to their death. It works with all characters in the game.
It is believed the glitch is related to how the Stage Builder generates terrain. On standard stages, any surface of two slopes must have a point that is connected to both slopes, as opposed to two points in the same place that are connected to each slope individually, or characters cannot walk smoothly between them. Should the Stage Builder see that a drop block and a sloped surface are adjacent, it may decide to fuse them together during the loading process, resulting in glitchy behavior if it does not realize they need to be separated once the drop block falls.
This glitch is unrelated to the Teleport glitch, another teleportation-based glitch involving drop blocks.