How to Get to the Boss in Leaf Green

Enter the Game Corner found in Celadon City. Talk to the Team Rocket grunt in the back of the arcade who is standing in front of a poster. Defeat his Raticate and Zubat in a Pokemon battle.

Walk up to the poster where the Team Rocket member was standing and inspect it by pressing the "A" button. A secret entrance appears on the wall. Enter the opening and continue to Team Rocket's Hideout.

Immediately walk down the stairs as you enter the first level of the basement. There are five Team Rocket thugs in this area, but you have the option to avoid them by directly walking down the next set of stairs.

Navigate the floor puzzle laid out before you in the second basement level. You must navigate a sequence of panels that send your Pokemon Trainer in the direction you step on. A long Team Rocket goon will attack you with his Raticate, Koffing, Grimer and pair of Zubat.

Pass through another floor panel puzzle to get through the third basement level of Team Rocket's Hideout. Keep an eye out for the two Team Rocket members who will harass you if you enter their line of sight.

Fight through the Team Rocket punks on the fourth basement floor. You will encounter several strong Pokemon, including Arbok and Sandslash. Talk to the Team Rocket member in the room located on the upper left for the key to the elevator.

Take the stairs back up to the third floor and insert the key into the red elevator door. Enter the elevator and select the fourth basement floor. This takes you directly into Giovanni's private office, where you will confront his Onix, Rhyhorn and Kangaskhan.