With Ash's journey complete in the anime, the fan made game "Pokémon Fire Ash" has been complete and one of the features it has due to it being based off the anime is a restricted battle I think it's called, and I love it.
Basically, when you face a gym leader, someone in a league, a battle frontier person, etc, you can only choose the same amount of Pokémon for the battle your opponent has out of your party of 6. Assuming it's not a full battle of course! It's only for main character opponents so it's still easy to level up your team with regular enemies. I think it really adds to the strategy element. Especially if you don't know what your opponent has outside of gym leaders who are known for their types.
I'd love to see it added to more games in future.