In most previous Pokémon games, your adventure began when you were entrusted with your first Pokémon by a Pokémon Professor. There are probably many players who will bring their first Pokémon from past titles to Pokémon X and Pokémon Y using Pokémon Bank and Poké Transporter.
In Pokémon X and Pokémon Y, it's not Professor Sycamore who gives you your first Pokémon. Instead, when you receive a Pokémon from the professor, you'll be able to choose from Bulbasaur, Charmander, and Squirtle! These Pokémon were the first three Pokémon you could start your adventure with in Pokémon Red Version and Pokémon Blue Version, released in North America in 1998, the very beginning of the Pokémon series! And now you'll be able to include them in your party once again.
All three of these Pokémon—Bulbasaur, Charmander, and Squirtle—will be able to Mega Evolve! First, of course, you'll have to fully evolve them into Venusaur, Charizard, and Blastoise. Now, many years after Pokémon Red Version and Pokémon Blue Version were first released, these classic Pokémon gain incredible Mega-Evolved forms!