Rexes are a special enemy in Super Mario World. One thing that makes them special is that you can normal jump bounce on them twice. The first bounce crunches them into a one tile form where they keep walking at a faster speed, then a second normal jump bounce can be performed off the rex again. Additionally, the Rex is the only enemy in Super Mario World that you can get a high bounce off of when you kill them with a spin jump. Kaizo levels will often utilize these unique characteristics to allow for new combinations of jumps and progressions.