Walkthrough
Directly before finding the portal pad on the 7th Floor of the Silph Co. Building that will lead you to Giovanni in the President's Room, you will run into your Rival yet again. Even though you currently have your hands full with trying to defeat Team Rocket, your Rival will insist on battling you. His Pokemon Team will be very similar to the last battle you had with him, except for the fact that he has evolved three of his Pokemon (including his Starter Pokemon). After defeating him, you will be able to advance to finding Giovanni.
Rival (Bulbasaur Chosen): Level 37 Pidgeot, Level 38 Exeggcute, Level 35 Gyarados, Level 35 Alakazam, Level 40 Charizard
Rival (Charmander Chosen): Level 37 Pidgeot, Level 38 Growlithe, Level 35 Exeggcute, Level 35 Alakazam, Level 40 Blastoise
Rival (Squirtle Chosen): Level 37 Pidgeot, Level 38 Gyarados, Level 35 Growlithe, Level 35 Alakazam, Level 40 Venusaur