I know it's not the best idea Lisa was trying Heatran can be caught at the top of Stark Mountain. When the player goes to Route 225, the rival and Crasher Wake will warn you about the Pokémon. If you go along the route normally, you will meet Buck, who will ask you to go on patrol for "goons in space suits", alias Team Galactic grunts. When you reach the mountain, there will be Galactic Grunts, who will head into the mountain. The player will have to follow them inside. Inside, the Galactic Commanders will challenge you to a battle, with Charon to escape to steal the Magma Stone. Buck soon arrives with his Claydol, and will heal your injured Pokémon. After Looker stops the theft of the Magma Stone and arrests Charon named Buck so that you can help him find the Magma Stone. Buck will then take the stone and leave Stark Mountain, causing the mountain to begin to act up. After you talk to Buck in his house, he will return to the mountain go put the stone back. Go back to the top of Stark Mountain and Heatran will be there in the place of the Magma Stone