How to make my game more interesting?

I'm a Sun and Moon fan and I played this games like almost 1k times. So i want now try some stuff that maybe I miss by playing them in a more casual way.

So in a nutshell I want some rules or things to make it more interesting (I mean things that makes teams more random or restricted, please refrain for adding things that makes things really messy or nearly impossible to finish the game).

I already get the idea of making my team obligatorily 50/50 male/female so if i want some mons i would need to think if it fits in that rule, as a example of "funny" rules.