You've just moved into a new town and saved the local professor from an angry Pokémon using one of his spares. He lets you keep it and you set off on a Pokémon challenge across the new Hoenn region to catch, trade, and battle Pokémon.
There are 135 new Pokémon in the Hoenn region, and a whole new set of items and attacks. Some Trainers will challenge you to two-vs-two battles, with some Pokémon strategies tailored specifically to this kind of battle.
You can also take part in the Pokémon Contest pageants, requiring you to blend berries and feed them to Pokémon, improving their Contest attributes and walking away with prizes.
A special edition of Pokémon Ruby & Sapphire. There are some fairly large additions to this game, such as the introduction of the Battle Island, and the new side-story centered on Rayquaza.
You can now be ambushed by two Pokémon Trainers at the same time, even if they're not stood beside each other, and there are some new battle animations.
Ruby Version
Sapphire Version
Emerald Version
The Game Freak development team can be found on vacation at the hotel in Lilycove City.
One of the new special attacks that can be learned by Pikachu is Volt Tackle. The Japanese name of this move is "Voltekker", which also happened to be the signature move of the hero in Game Freak's "Pulseman" on Sega Genesis.
Pokémon Stadium Series