Quick Attack is Pikachu's Up B move.
Pikachu does a quick dash in one direction, and then if one tilts the control stick, Pikachu can dash in a second direction. In Super Smash Bros., this attack did no damage. Starting in Super Smash Bros. Melee, Pikachu can do light damage to characters he passes through. The attack has a huge range, but the second jump requires a minimum or a 35 degree change in turn, and, although it is executed very quickly, it has some lag during the start and end. It is, overall, extremely difficult to control.
Quick Attack is a Pokémon move that does light damage, and always goes first (if two such moves are used, the Pokemon with higher speed goes first, as if it were a normal battle).