Rain, rain, rain. Find yourself up against team full of bulky or fast swift swimmers unprepared and prepare to feel pain. You would have to counter somehow, by either bringing out your own weather setter or setting up Trick Room. Cresselia works really well here so I would suspect its usage will skyrocket. It can tank both physical and special attacks fairly well and set weather so it's a potential weather counter against many weather teams but especially useful against rain teams because of the sheer number of swift swimmers. Actually, Cress can counter sun and tailwind teams for the same reason. Sandstorm teams may actually up in usage because of Cress. Tyranitar to set sandstorm and counter Cress (Pursuit or no), the rest of the team to take advantage of Trick Room if it's a trick room set.