Landorus-Therian (M) @ Power Herb
Ability: Intimidate
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Earthquake
- Fly
- Stealth Rock / Stone Edge
- Swords Dance
You basically use Swords Dance on the switch and hit Fly, it will activate in one turn and OHKOs Rillaboom.
+2 252 Atk Landorus-Therian Fly vs. 240 HP / 0 Def Rillaboom: 696-822 (173.5 - 204.9%) -- guaranteed OHKO
252+ Atk Rillaboom Grassy Glide vs. 0 HP / 0 Def Landorus-Therian in Grassy Terrain: 174-205 (54.5 - 64.2%) -- guaranteed 2HKO
I am around 72.6% sure that this isn't a lure. But here goes.
Rindo Berry Mamoswine!
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Ability: Thick Fat
EVs: 232 Atk / 80 Def / 196 Spe
Jolly Nature
- Icicle Crash
- Ice Shard
- Earthquake
- Stealth Rock
Ice Shard on the switch. Rillaboom, while it will feel that Ice Shard, will likely stay in and Grassy Glide, expecting it to OHKO. But no! Rindo Berry makes it a 2HKO, and you can either Ice Shard or Icicle Crash to take out the Rillaboom. Additionally, if for some reason they try to Superpower, the given EV spread lets it survive and take it out with two Ice Shards. Finally, 196 Speed and a Jolly Nature outspeed Rillaboom anyways, so Grassy Glide into Superpower would not KO before Ice Shard into Icicle Crash.
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Grassy Glide vs. 0 HP / 80 Def
in Grassy Terrain: 174-205 (48.1 - 56.7%) -- 37.1% chance to 2HKO after Grassy Terrain recovery
252+ Atk
176 Atk Mamoswine Ice Shard vs. 240 HP / 4 Def Rillaboom: 134-162 (33.4 - 40.3%) into 176 Atk Mamoswine Icicle Crash vs. 240 HP / 4 Def Rillaboom: 288-338 (71.8 - 84.2%) = (95.2 - 114.5%) -- ~75% to KO
Reserving sashed Weavile
Focus Sash Weavile
Weavile @ Focus Sash
Ability: Pressure
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Triple Axel
- Knock Off
- Ice Shard
- Swords Dance
Priority is the bane of many fast pokemon. Weavile, bring the frail ass that it is, is no exception. This lure best works if you get a safe switch into something it can revenge kill. Once Rillaboom gets a safe switch in, just use triple axel. Rillaboom will try to grassy glide Weavile before getting OHKO'd by triple axel.
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I mainly scrapped this because swords dance rillaboom just uses it as set up fodder and Slowbro can do nothing but hope for a scald burn. It only works on a banded rillaboom if it uses grassy glide instead of wood hammer. Wood hammer just OHKOs and if the opponent is using damage calcs, you're basically dead.
Slowbro @ Heavy-Duty Boots
Ability: Regenerator
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
IVs: 0 Atk
- Future Sight
- Counter
- Slack Off / Scald
- Teleport
@ Occa Berry 
Aerial Ace Kartana 
Ladies and gentlemen...my third lure!
Ability: Beast Boost
EVs: 152 HP / 100 Atk / 156 SpD / 100 Spe
Adamant Nature (+Atk, -SpA)
Close Combat
Leech Life
Rock Tomb
Roost
Normally, Buzzwole would have nothing to hit Volcarona with since it runs Ice Punch, which incentivizes it to come in and setup. The main point of this set is that Rock Tomb is good for not only Volcarona, but also checks such as Zapdos. Additionally, it negates Dragonite's Speed boosts from Dragon Dance and its Multiscale, while hitting the same Flying-types that Ice Punch hits. Occa Berry lets it survive an unboosted Fire Blast from offensive QD Volcarona, while the given EVs let it take a +1 Psychic from bulky QD Volcarona. 100 Speed lets it always outspeed -1 bulky Volcarona.
Other Options
You can run Stone Edge to OHKO bulky Volcarona, but it comes at the cost of missing and just losing to either set. Additionally, you lose the utility that Rock Tomb provides.
Calculations
+1 252+ SpA Volcarona Flamethrower vs. 152 HP / 156 SpD Occa Berry Buzzwole: 324-382 (82.4 - 97.2%) -- guaranteed 2HKO
100+ Atk Buzzwole Rock Tomb vs. 0 HP / 4 Def Volcarona: 384-456 (123.4 - 146.6%) -- guaranteed OHKO
100+ Atk Buzzwole Rock Tomb vs. 248 HP / 156 Def Volcarona: 316-372 (84.7 - 99.7%) -- guaranteed 2HKO
100 Speed Buzzwole - 219 Speed, while -1 252 Speed Volcarona - 218 Speed
Kartana @ Protective Pads
Ability: Beast Boost
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Leaf Blade
- Knock Off / Sacred Sword
- Aerial Ace
- Swords Dance
Volcarona is more than happy to switch into Kartana and threaten to burn it, and then gets promptly blown away with +2 Aerial Ace, as bulkier Volcarona spreads live every hit otherwise. Alternatively, any other move + Aerial Ace will take out the provided Volcarona spread if you cannot afford to boost. This also has the added bonus of being an excellent Buzzwole lure. If you want to be less cute abut it, Adamant +2 Knock Off or Life Orb Knock Off also do the trick, but Kartana is more at risk, especially if it cannot afford to SD.
+2 252 Atk Kartana Aerial Ace vs. 0 HP / 0 Def Volcarona: 476-562 (153 - 180.7%) -- guaranteed OHKO
+2 252 Atk Kartana Aerial Ace vs. 248 HP / 156 Def Volcarona: 386-456 (103.4 - 122.2%) -- guaranteed OHKO
Power Herb + Solar Beam Charizard 
252 SpA Charizard Hurricane vs. 0 HP / 0 SpD Barraskewda: 276-325 (104.9 - 123.5%) -- guaranteed OHKO 
252 SpA Charizard Solar Beam vs. 0 HP / 0 SpD Barraskewda: 400-472 (152 - 179.4%) -- guaranteed OHKO 252+ Atk Choice Band Barraskewda Liquidation vs. 0 HP / 0 Def Charizard: 542-638 (182.4 - 214.8%) -- guaranteed OHKO 252+ Atk Choice Band Barraskewda Flip Turn vs. 0 HP / 0 Def Charizard: 384-452 (129.2 - 152.1%) -- guaranteed OHKO 
Focus Sash Landorus-Therian
Ferrothorn @ Chople Berry
Ability: Iron Barbs
EVs: 252 HP / 4 Atk / 252 Def
Impish Nature
- Power Whip
- Knock Off
- Leech Seed
- Spikes
After enough chip damage, Barraskewda has the ability to get into an OHKO range and usually press Close Combat. This allows Ferrothorn to suprise it with a Chople Berry and obliterate it with a Power Whip.
252+ Atk Choice Band Barraskewda Close Combat vs. 252 HP / 252+ Def Ferrothorn: 248-292 (70.4 - 82.9%) -- guaranteed 2HKO
252+ Atk Choice Band Barraskewda Close Combat vs. 252 HP / 252+ Def Chople Berry Ferrothorn: 124-146 (35.2 - 41.4%) -- guaranteed 3HKO
0 Atk Ferrothorn Power Whip vs. -1 0 HP / 4 Def Barraskewda: 558-656 (212.1 - 249.4%) -- guaranteed OHKO
i said i’d do something stupid, so…
Charizard @ Power Herb
Ability: Blaze
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Fire Blast
- Hurricane
- Solar Beam
- Roost
I promised stupidity, which I shall now provide.
The only required move here is Solar Beam; it takes care of Barraskewda and other pesky Water-types on the switch, but it only really has one use, and it relies on prediction, especially under rain. If you're under rain, yet there's still some dangerous Water-types, then Hurricane also takes care of Barraskewda on the switch. But why would you use Solar Beam under rain?
Again, this is just plain stupid. But that's the point. I'm simply fulfilling my promise.
Just pray that you predict the right switch. But why would you use Charizard in OU, specifically this one? Just why?
Landorus-Therian (M) @ Focus Sash
Ability: Intimidate
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Earthquake
- Stone Edge
- Rock Polish
- Swords Dance
Barreskewda is a weird Pokemon to lure, as it basically never wants to switch into anything that could possibly KO it, which is most Pokemon due to how frail it is. Which leaves eating a hit with a resist berry or focus sash and KOing back the main way of luring it. I went with Focus Sash Landorus-Therian as it very rarely runs an offensive set. Barreskewda will come to force Landorus out or revenge kill after it sets up, only to get KOed by Earthquake. This obviously only works on an HO team that can pressure the rain team enough to keep off hazards. Barreskewda might be the only Pokemon on a rain team that out-speeds Landorus after a Rock Polish as well, which aids in the lure. The main caveat here is that they just use Flip Turn, but there isn't much way to get around that.
252+ Atk Landorus-Therian Earthquake vs. 0 HP / 4 Def Barraskewda: 292-345 (111 - 131.1%) -- guaranteed OHKO
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