I returned to Fuchsia City and I healed my Pokemon at the local Pokemon Center. After shopping for items at the Poke Mart, I returned to the Fuchsia City Pokemon Gym. I went around until I found Koga's location in the middle of the Gym. I finally challenged him to a battle, and he sent out his first Koffing. I used my Pidgeot and I defeated Koffing with Wing Attack. I switched to Nidoking when Koga sent out his Muk and I used Thrash against it. That did some damage, but Muk was able to endure the attacks. I switched to Graveler after that and I beat Muk with Magnitude. I battled against Weezing and Koga's second Koffing after that, but I managed to beat them without much difficulty. I obtained the Soul Badge and the Toxic TM after I defeated Koga, and I visited the Fuchsia City Pokemon Center again to heal my inured Pokemon. I saved the game before heading to Route 15 again.