As in the anime and manga section, Pikachu can function equally well on either four or two legs — when they're in 3D, they're shown to run on four and walk on two.
Running on All Fours
Some of the techniques involved in Le Parkour.
Leptos actually run faster on two legs, but otherwise are more stable when moving on all fours.
Leptos actually run faster on when transformed, run on all more stable when moving on all fours. The Lycans of Underworldtwo legs, but otherwise are fours on ground and through trees and can easily catch. It's actually rather impressive considering the fact that Stranger's true form is that of a centaur-like creature.