Shuckles, I'll try and give you something fun.
Take a Drifloon.
If it is male, it may evolve after the 5th gym. If it is female, it may evolve after the 4th gym.
If its ability is Aftermath, it must know Payback. If its ability is Unburden, it must know Ominous Wind.
If it has a +Atk nature...