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.
It can be quite confusing. Horse registries have height requirements for their breed standards. So do some show registries. They most all state that anything under 14.2 is a pony. The Arab is a small horse, I have some 14.1 individuals. They look like ponies, but they are horses and are registered as such. If a pony breed allows it, ponies can be in the 15 hand range.