I think it would be cool if the first and last gym leaders were from like say Sinnoh and Jhoto (just for example). And one had a new evolution for Donphan and the other had a new evolution for Medicham.
Just came up with something...
What if the first gym was ground so fire was weak, the second was steel so grass was weak, and the third was grass so water tyoe was weak.
Fire does neutral damage to ground, takes double from ground ofc but idea isn't bad