[X] Magneton - Putting Magneton up against a major type mismatch, they would be pushed to their limits although unlike Forretress they only have one way to extend the battle.
[X] Forretress - While she'd almost certainly lose quickly, there are a few tricks you could try to drag it out giving her experience against type mismatches.
[X] Dragonite - Keeping Dragonite in will allow him to learn how to properly fly and adapt to his new body. Although that could also be done via standard training.