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.
Horses vs. Ponies. Size is a factor differentiating horses and ponies; the maximum height for ponies is 14.2 hands, and for miniature horses it's 8.5 hands. However, miniature horses are specifically bred to look exactly like their larger namesake, whereas a pony need not resemble a specific breed. Several distinct pony breeds exist, including the Shetland -- the strongest pony of its size -- and the Chincoteague.