What are the Halloween costumes called ware you look like you are riding a horse or somthing but you are not?

Those Halloween costumes are typically called "riding" or "mounted" costumes. They often feature a design that makes it appear as though the wearer is riding a horse, dinosaur, or other large animal, with the legs of the costume designed to mimic the animal's legs. These costumes are popular for their humorous and whimsical effect, creating an illusion without the need for an actual animal.