Wailord needs entry hazards set up on the opponent's side of the field to be effective, as foes can switch around without much trouble otherwise, limiting its PP stalling abilities. Don't be afraid to use Wailord's natural bulk to switch in on threats it can wall, such as Torkoal.
A pony is not a small horse. Horses and ponies are genetically two different species. There are horse-sized ponies, and pony-sized horses, but the genetics are what tells them apart, not the size. A miniature horse, for example, is very small and looks like a pony, but genetically, it is a horse.
The typical maximum height of the horse, which is measured in hands. A hand is equivalent to 4 inches (101.6 millimeters). An animal under 14.2 hands is usually classified as a pony, while an animal with a height over 14.2 hands is considered to be a horse. Miniature horses tend to be around nine hands or less. Maximum height helps classify the type of animal, and some disciplines require tall or shorter breeds.