Pikachu is much stronger than he was before. His smashes are all very good. His down smash is perfect for setting up for juggles, and his front smash has range, priority and power. His aerials are all very fast. Pikachu can easily juggle opponents with thunders and fast aerials.
Pikachu's one disadvantage is that he is outranged in the air. Think of Marth's sword slashes against Pika's aerials. Marth has both priority and range advantages
Pikachu shoots forward. The longer you charge this attack, the farther he'll go.
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Quick Attack
He dashes in any direction. Input another direction to make him dash again.
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Thunder
He calls down a thunderbolt. It's quite powerful, but will not pass through platforms right above Pikachu's head. If the platform is a good distance above Pikachu, the thunderbolt will travel through platforms and terrain. if the bolt hits Pikachu, it will use a powerful proximity attack that deals more damage than the standard bolt. Don't make yourself predictable and spam this though, as an opponent can easily wait to punish the cooldown lag. This attack can also be reflected and absorbed (like with Lucas's or Ness's PSI Magnet).
Volt Tackle: Pikachu transforms into a huge sphere of electricity that you can move around the screen to hit anything in the path, plus Pikachu gains the power to go through platforms. Press to make Pikachu Spark, damaging anyone in the vicinity. This attack lasts about 15 seconds, and will do around a good 60-80% damage. However, this attack is hard to control, much like Sonic's Final Smash.