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.
1 The FEI definition of a pony is in accordance with A rticle 3103.1.  Nevertheless, to allow for the f ct that FEI pony measurement takes place under competition conditions ponies measured at competition must not exceed 150cm without shoes or 151cm with shoes in o rde r to be permitted to compete.