Thunder Jolt is Pikachu and Pichu's Neutral B move.
Unlike most other attacks Pokémon use in Super Smash Bros. games, Thunder Jolt is not the name of an attack also used in the Pokémon RPGs. It is likely that "Thunder Jolt" is a misnomer and that the attack's actual name is supposed to be "Thundershock", the basic Electric attack that Pikachu and Pichu can use in the RPGs.
Use this ground hugging projectile attack while standing and jumping. It also damages Pichu to use it, however.