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1. Poison
2. Bug
3. Grass
4. Electric
5. Ground
6. Fire/Fight
7. Ice
8. Water
But I'd suggest not being too focused on the gym battles. There are plenty of other battles that are arguably even tougher.
I completed the game and had a few questions I couldn't figure out.
1. Where do you get Registeel?
2. Which move is taught by the witch South of Frozen Dunes? None of my mons could learn it.
3. What's with the lighthouse horror stories across the different regions? Tohio or something? Is it...
I completed the game (V2.2) and I noted down a lot of info about things like pokemon & item locations. The file is zipped and attached for anyone interested.