With the addition of the Crown tundra, some Pokemon have certainly shown themselves to be serious threats. I will probably miss a few, however, these are some that I have seen quite a bit, and I can see why they are powerful.
In OU, Zapdos has a high usage rate with 18.99% usage rate (top is spread out with a lot it is pretty big ok? ok.) . The offensive set from Smogon reads as follows
Zapdos @ Heavy Duty boots
EVS: 4 Def / 252 SpA / 252 Spe
Volt Switch / Roost
Heavy Duty boots is for entry hazards. Thunder and Hurricane is stab. This seems to be fitting in a rain team, as Hurricane and Thunder cannot miss in the rain. Weather ball would be water coverage in the rain to take out threatening rock types such as tyranitar. Roost is recovery and Volt switch is a pivot.
Magearna @ Life Orb
Ability: Soul Heart
EVS: 252 SpA / 4 SpD / 252 Spe
Aura Sphere / Focus Blast / Draining kiss
This set is one of my favorite magearna sets. It has a usage rate of 23.99% in OU. Shift gear is to make it faster, (and boost it's attack but you will never use physical attack on magearna you fool), Calm mind is to boost Special attack and Special Defense. Stored power is a brilliant addition on to this set. I will use the Stored power calculations on a very common Pokemon that is weak to stored power: Toxapex. Here they are: The first one will be using stored power on a toxapex, WITH one calm mind used. Standard EVS will be used for toxapex. +1 252 SpA Life Orb Magearna Stored Power (60 BP) vs. 252 HP / 4 SpD Toxapex: 190-224 (62.5 - 73.6%) -- guaranteed 2HKO. That is quite good. Now, let's look at shift gear. 252 SpA Life Orb Magearna Stored Power (80 BP) vs. 252 HP / 4 SpD Toxapex: 169-200 (55.5 - 65.7%) -- guaranteed 2HKO. If you manage to get off a shift gear and a calm mind, well, chuckle, +1 252 SpA Life Orb Magearna Stored Power (120 BP) vs. 252 HP / 4 SpD Toxapex: 374-442 (123 - 145.3%) -- guaranteed OHKO. Keep in mind this Pokemon has Life orb. For the final moves, I would prefer Draining kiss as it's stab, but your decision really.
One more Special sweeper then on to the physicals.
Ahh Spectrier. You broken beast.
Spectrier @ Leftovers
Ability: Grim Neigh
EVS: 112 HP / 20 Def / 172 SpA / 20 SpD / 184 Spe
Hex / Shadow Ball
Calm mind / Nasty Plot / Taunt
Will-O-wisp / Disable / Dark Pulse
Usage rate in OU is 14.16% There are a variety of things you can do. One thing that is basically mandatory, however, is if you choose hex, you MUST chose will-o-wisp. Subsitute is to take a hit or two while setting up, Hex / Shadow Ball is stab, Calm mind is a status that boosts SpA and SpD by one stage, and Nasty Plot is SpA by 2 stages. So really, it is the difference between frail and strong or a bit less strong but a bit bulkier (NOT TO BE USED AS A TANK). Taunt is for hazard setters or deffoggers. Will-O-Wisp is to be paired with hex, disable is to disable moves and Dark Pulse is coverage. One thing that people don't realize is that hex can be QUITE deadly. Let's look on toxapex, which this move isn't even super effective on. 0 SpA Spectrier Hex (130 BP) vs. 252 HP / 4 SpD Toxapex: 142-168 (46.7 - 55.2%) -- 99.6% chance to 2HKO after burn damage. This is not super effective. If you use calm mind on your set, +1 0 SpA Spectrier Hex (130 BP) vs. 252 HP / 4 SpD Toxapex: 213-252 (70 - 82.8%) -- guaranteed 2HKO after burn damage. If you use nasty plot, +2 0 SpA Spectrier Hex (130 BP) vs. 252 HP / 4 SpD Toxapex: 283-334 (93 - 109.8%) -- 56.3% chance to OHKO. You should be able to see how potent Hex can be.
I have not been in the competitive seen much before, but I have heard horror stories about Landorus therian ripping apart people's teams. Nice.
Landorus-Therian @ Leftovers
EVs: 252 Atk / 4 Def / 252 Spe
- Swords Dance
- Stone Edge
- Stealth Rock
This is a very good set, and a good Pokemon. Usage rate in OU of 31.74%. It is interesting to me that there isn't flying stab in this set, but I think it may just be the lack of flying stab that Landorus can learn. Swords dance is to setup, Earthquake is by far in my opinion the best physical ground type move, stone Edge is coverage and Stealth rock is a hazard. To prove my earthquake point, MORE CALCS!!! Toxapex is our premier target. (I'm not using clefable as a tank because it can also be used in different ways, where toxapex is just a wall). Without a swords dance: 252 Atk Landorus-Therian Earthquake vs. 252 HP / 252+ Def Toxapex: 188-224 (61.8 - 73.6%) -- guaranteed 2HKO. With Swords Dance: +2 252 Atk Landorus-Therian Earthquake vs. 252 HP / 252+ Def Toxapex: 378-446 (124.3 - 146.7%) -- guaranteed OHKO.
Cinderace @ Heavy-Duty Boots
EVs: 252 Atk / 4 SpD / 252 Spe
- Bulk Up
- Pyro Ball
- Zen Headbutt
- Sucker Punch
I like more offensive sets, so yeaah. Bulk up is to raise attack and defense, pyro ball is stab, Zen Headbutt is coverage and Sucker punch is priority. Zen Headbutt can help deal with toxapex. 252+ Atk Libero Cinderace Zen Headbutt vs. 252 HP / 252+ Def Toxapex: 144-170 (47.3 - 55.9%) -- 78.5% chance to 2HKO. Without a Bulk up? Not that good. With one? Much better. +1 252+ Atk Libero Cinderace Zen Headbutt vs. 252 HP / 252+ Def Toxapex: 212-252 (69.7 - 82.8%) -- guaranteed 2HKO. So yeah
Urshifu @ Black Glasses
Ability: Unseen Fist
EVs: 252 Atk / 4 SpD / 252 Spe
- Bulk Up
- Wicked Blow
- Close Combat
- Sucker Punch
THIS is my kind of set. Spam one move and kill everything. Nice. Bulk up to help murder everything in sight, Wicked blow to crit the crap out of everything, Close combat for a powerful fighting stab move and Sucker punch for priority. For perspective, let's test against toxapex. 252 Atk Black Glasses Urshifu Wicked Blow vs. 252 HP / 252+ Def Toxapex on a critical hit: 127-150 (41.7 - 49.3%) -- guaranteed 3HKO. Not that good. With a Bulk up though, +1 252 Atk Black Glasses Urshifu Wicked Blow vs. 252 HP / 252+ Def Toxapex on a critical hit: 187-222 (61.5 - 73%) -- guaranteed 2HKO.
These are all of mine, I hope they're good and they help people who read this thread.