Not only will this harm an enemy, it also has a 10% chance of Paralyzing the opposing Pokémon as well.
In Super Smash Bros.
In the Super Smash Bros. series, thunder shock is one of Pikachu's and Pichu's smash attacks. It'll inflict a great amount of damage to your opponent - 10%-28% for Pikachu, though only 1-20% for Pichu. It should also be noted that this attack will harm Pichu as well.
By leveling up
By Special move