Locate the trainer Doctor Derek first and use the stairway near him to reach the section of BF1 where Heatran's chamber is located. Once you are ready, save and then use the Magma Stone to unveil Heatran then interact with it to face him in battle. Once in battle, paralyze it and then weaken it as best you can with moves that do neutral damage to Heatran. Then swap in a good Water-type to help take the damage from the Fire and Steel-type moves as you try to catch Heatran.
The Nature Preserve was established as a secret haven for Pokémon, so far away from Unova that the only way to reach it is by airplane from Mistralton City. The grove is home to many kinds of Pokémon that cannot be found anywhere else, including some that have reached level 100!
Go south from the plane and head east through the trees. Soon you reach a clearing, and in the middle of it, a ShinyHaxorus! Its body may be colored differently, but its stats are the same as those of a normal-colored one. Catch it if you can!
The Elite Four and Champion have grown even stronger since you first battled them. They now have more Pokémon, and their levels have increased significantly. Gather a team of superior Pokémon before challenging them again! By fulfilling certain requirements, you can earn up to 19 Medals by battling these same five people, so get going!
Iris' Pokémon are nearly 20 levels higher than they were during your first battle. Take out her three powerful dragons quickly with Ice moves like Ice Beam and Blizzard. Her Archeops is also vulnerable to Ice attacks. Switch Pokémon when Lapras and Aggron appear in order to strike with super-effective moves. Aside from their individual weaknesses, the two share a weakness to Fighting-type attacks.