What are some changes that you would make to the mechanics or particular moves if you had the chance? To get the ball rolling here are a few of mine.
Change toxic back to 100% accuracy but if used by a non poison type pokemon it only inflicts poison.
Using Toxic on a pokemon that is already poisoned will change it into Toxic.
Change paralysis so that when it activates you get -6 speed for that turn rather than losing the whole turn.
Change freeze so that it works like paralysis does now and when it activates you lose the turn.
Roost only gives you 25% health back when you use it and you don't get the other 25% until the end of the turn.
Bring back pursuit but make it uneffected by typing.
Feint ignores the effect of psychic terrain.