Volt Tackle (move)
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Volt Tackle is a lucrative move available in Pokémon Emerald. Here are the stat details:
Unfortunately, there is only way to get Volt Tackle. You need to obtain a Pikachu or Raichu, a Light Ball, and either a Pikachu/Raichu of a different Gender, or a Ditto. Attach the Light Ball to the/a Pikachu, and give both to the Day Care Lady. When they eventually mate and produce an egg, the eventual Pichu that shall hatch will have Volt Tackle.
If you wish to spread Volt Tackle, then you shall need to make Pichu evolve, then breed onto another Pokemon that is capable of learning it