Make a game mod based on notable/tough gym leaders and Elite Four.
Example:
Brock: infamous first Gym battle where you need Squirtle/Bulbasaur for your starter OR get a Mankey or Butterfree with confusion Whitney: Battle with Miltank's rollout is stupid difficult early on. Winona: Having Skarmory and Altaria is a really difficult to counter. Sabrina: Psychic Gym leader in a time where there was no good counter type. Steven: Metagross is difficult! Lance: Dragon types have ice weakness in gen 1, but Dragonair and Dragonite face little challenge then. Also Lance is badass. Cynthia: Garchomp. Need I say more.