Gotta catch even more!

Enter a whole new world, with new Pokémon to capture, train, and battle!  Meet Professor Elm and get the all-new Poké Gear, including map, radio, cell phone, and clock.  Set the clock then watch as day turns to night and events take place in real time -- and be sure to keep an eye out for Pokémon that only come out at night!

• Dozens of never before seen Pokémon!  Find new evolutions for some familiar Pokémon and discover whole new species.  Your Pokédex will even reveal genders of some Pokémon.
• A whole new world!  Explore Johto, where there are new gym leaders to beat and eight new badges to earn.
• Two new types!  Introducing Dark- and Steel-type Pokémon.
• Trade with Gold, Silver, Red, Blue, and Yellow to catch 'em all! (Requires Game Link cable, sold separately.  New Pokémon cannot be traded back to Blue, Red, or Yellow versions.  Not compatible with Pokémon Stadium.)
• Compatible with Pokémon Pikachu 2 GS!

Source - Back of box