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 traditional standard for height of a horse or a pony at maturity is 14.2 hands (58 inches, 147 cm). An animal 14.2 h or over is usually considered to be a horse and one less than 14.2 h a pony, but there are many exceptions to the traditional standard.