If you haven't played rain since the last round of bans yet, give it a try. It has everything it needs to be just as deadly as it was last gen (well, except Kingdra). In fact it now has Volcanion and Araquanid to act as breakers that are way stronger than what we've had before, and both these Pokemon additionally absorb opposing rain boosted moves to help your team (Volcanion outright, and Araquanid by virtue of insane special bulk + Scald burn immunity). These in addition to other breakers like Thundurus (both forms), Tornadus-I, Keldeo, and various Z-move users make it very easy to break fatter builds. For example, NP Thundurus T with Z Focus Blast + one of Ludicolo/Volcanion/Keldeo is an easy way to deal with stall. And of course, it's almost impossible for offense to stop Kabutops and Ludicolo from just getting multiple kills in a row since the rain boost essentially invalidates a lot of offensive water resistances. It's especially effective when they can be supported by good rain options like Breloom, Celebi, and Forretress. Of course all this is only made possible by automatic 8 turn rain, as clearly manual rain wouldn't be anywhere near as effective.
Drought doesn't seem to be as effective, but I haven't tried it out since before Dragonite and company were banned, and even then I didn't try that hard to make it work before I moved onto something else. I won't be nominating it this round, and I'm curious to see if it actually ends up broken, but it is something to keep an eye out for.
