Walkthrough
After defeating the Elite Four, you will be able to complete the Post Game Master Trainer Challenge. Scattered across the Kanto Region, there will now be trainers that specialize in using one specific species of Pokemon. By defeating them, you will earn the Master Title for that specific Pokemon Species. However, you will only be able to battle these Master Trainers with the Pokemon they specialize in using. On top of this, their version of said Pokemon will be at an extremely high level, and some will even know special moves that given Pokemon Species can't usually learn.
If you want to know where to find all the Master Trainers found in the Post Game, you can click on every page apart of our Ultimate Walkthrough Section within this Guide! That, or simply check out our Where Are All The Master Trainers Page!