Ok. I've been playing around on Showdown. Here's some cores I've been experimenting with.
First, a new defensive rain core.
While Politoed's rain isn't eternal like it used to be, Physically Defensive Damp Rock Politoed still causes eight turns of rain on the switch and can use moves like Scald, Toxic, Hypnosis and Perish Song to support the team further.
Priority Rain Dance on Specially Defensive Klefki will serve as a viable second rain setter. Klefi's great defensive typing covers a lot of threats, and its Fire weakness is neutralized by the rain. Furthermore, it is free to use its other priority support moves like Spikes, Thunder Wave, etc.
Physically Defensive Zapdos covers the grass weakness of Politoed (and assuming Lightningrod ever gets release, will be able to use that as well to cover its electric weakness.) Zapdos also covers Kleki's ground weakness. Zapdos is also notable in this core because it has access to near perfect coverage with 100% rain accurate Thunder and Hidden Power Ice, and has the now buffed Defog for hazards as well as Roost for healing.
These three together will ensure the majority of the game will have rain present, and with Swift Swim now allowed with Drizzle, feel free to take advantage of the good synergy these guys have with Kingdra, Ludicolo, Kabutops and Omastar, along with all your other favorite rain mons including Azumarril, Greninja, Dragonite, Goodra, Noivern, Hurricane Volcorona, Heliolisk, Toxicroak, and Jynx.
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Offensive core.
Swords Dance Talonflame is so stupidly good. Taking advantage of priority, I invested in some some bulk, Flying Gem Acrobatics, Flare Blitz and priority Roost. It's just madness.
Sash Dugtrio murders Tyranitar and Heatran for Talonflame, and many grounded steel types that wall Scizor. Stone Edge can OHKO any opposing Talonflame.
Bulky Defog Scizor provides both of them with Bulk+Defog+Roost support keeping the rocks away, and can keep offensive momentum by using Bullet Punch and U-Turning away from any incoming Fire or Steel type to feed the kill to Dugtrio.
Rotom W and dedicated physical walls beat all three of these guys still, but I'm not making your whole team for you. Dammit. ;)