First of all let me say that this is a really interesting thread and a great idea (thank you progenitor). I tend to get lots of new ideas and can share my own!
Electrics and Bugs
Molk and ScraftyIsTheBeast have both brought up different types of Pokemon to look at: Electric and Bug, respectively. My favorite of each type is probably the one that shares these two types: Galvantula!
Galvantula (M) @ Life Orb
Trait: Compoundeyes
EVs: 4 HP/252 SpA/252 Spe
Nature: Timid
-Thunder
-Bug Buzz
-Volt Switch
-Giga Drain
With two very powerful STABs and an ability that greatly amplifies one of them, Galvantula is not to play around with. Much of RU is hit neutrally, and Thunder's 91% accuracy and 30% paralysis rate make it quite spamm-able. Volt Switch allows Galvantula to pivot out of things such as Magmortar and Typhlosion. Lastly, Giga Drain hits Ground-types very hard, especially Rhydon. Despite having a recovery move, however, Galvantula is worn out very quickly due to its SR weakness. That's why a spinner is important. Generally, between the two spinners of RU (Armaldo and Torkoal don't count, and aren't as good either), Kabutops has much better synergy with Galvantula than Cryogonal:
Kabutops (M) @ Life Orb
Trait: Swift Swim
EVs: 4 HP/252 Atk/252 Spe
Nature: Jolly
-Stone Edge
-Rapid Spin
-Waterfall
-Aqua Jet/Swords Dance
Despite Kabutops having to give up a key move (priority, spinning, setup, or a powerful STAB move), it functions very well, having great power after a LO boost. It is chosen over Cryogonal since Kabutops is stronger offensively, and Cryogonal and Galvantula share two weaknesses.
Defensive synergy:
Galvantula:
Fire- Kabutops 4x resists
Rock- Kabutops is neutral, but Waterfall is super-effective
Kabutops:
Grass- Galvantula resists
Fighting- Galvantula resists
Ground- Galvantula resists; both Pokemon carry a move to hit these super-effectively
Electric- Galvantula resists; most are hit hard by STAB Bug Buzz
This is a good offensive core in general, and under rain (provided by a good defensive Pokemon such as Uxie or some Druddigon/Hariyama variants), Kabutops becomes a ferocious sweeper with a Swift Swim boost. In these cases it is a good idea to run Swords Dance.
New Hail Abuser
Yes, pretty much every Ice-type gets Blizzard, but many more Pokemon do, most notably Water-types. One that is overlooked is Choice Specs Feraligatr (yes I have tested it):
Feraligatr (M) @ Choice Specs
Trait: Torrent (Sheer Force when released)
EVs: 252 HP/252 SpA/4 Spe
Nature: Modest
-Hydro Pump
-Blizzard
-Focus Blast
-Hidden Power Fire
Even with Feraligatr's fairly low special attack, with maximum investment and Choice Specs, it hits surprisingly hard. Hydro Pump is the preferred STAB to maximize damage output; the 120 BP is nothing to play around with. Blizzard is the secondary move, safe to spam under Hail, and hitting things such as Druddigon, Lilligant (on the switch-in), and many others, very hard. Focus Blast is really mainly for when Feraligatr has to combat Water-types and Clefable, and isn't used much otherwise due to the shaky accuracy. Finally, Hidden Power Fire was chosen to hit Ferroseed and Escavalier harder than it can with physical moves, easily outspeeding both despite almost no speed investment.
When Sheer Force is released, it should immediately replace Torrent on this set for the 33.3% boost to Blizzard and Focus Blast, while removing side effects that occur only 10% of the time anyway.
So do you think this is a viable Hail abuser outside of being a surprise factor, or is it just a gimmick? Is Ferliagatr best using its standard physical sets? You decide!
Physical Cleaners
Many great physical sweepers, specifically cleaners, have amazing offensive presence, but need a speed boost or certain checks/counters weakened or removed before starting their rampage. Some that come to mind:
Which of these (or another one you can think of) is your favorite and why? Which of these has major setbacks or the like? Which of these need more team support?
NOTE: Torterra is only really a cleaner with Rock Polish, and Emboar only with Choice Scarf.