Building Gym and Elite 4 Teams

I'm making my own fan game and need help planning the teams for the gym leaders and elite 4. The leaders and the 4 are all the ones from generation 1, but any Pokémon from any gen is allowed. They'll all have 6 pokemon and I'd like them to fit the following criteria as closely as possible.

1: A Pokémon that can Mega Evolve 2: A Pokémon to terastalize 3: A Pokémon to Dynamax 4: A legendary or Sub Legendary 5: A fusion (Both components don't have to match the trainers type. EX: Brock could have a Golem x Blissey and that would be acceptable. ) 6: Whatever Pokémon doesn't meet the terms for the first 5, but would fit on the team if it's stats we're doubled.

I'm hoping the discussions down in the comments can help me work out some good teams and ill answer questions people might have down below in comments as well.