Crawdaunt, the Red Lobster Pokémon. Unlike its counterpart Kingler, Crawdaunt is more specially offensive, at the cost of physical bulk and speed. However, that's not what we care about, Adaptability turns Crawdaunt into an Utter monster, able to cleave through unprepared team with little notice. Its frailty and the existence of Dracovish mean that Crawdaunt is somewhat predictable and outclassed, but it can still perform well with the right team support.
Case Closed! Bring Out the Dancing Lobsters!
Crawdaunt
Ability: Adaptability
Item: Life Orb/Mystic Water
-Dragon Dance/Swords Dance
-Crab Hammer
-Knock Off
-Aqua Jet/X-Scissor/Close Combat
Nature: Jolly (+SPE, -SATK) or Adamant (+ATK, -SATK)
EVs: 4 HP/252 ATK/252 SPE
Crawdaunt gets access to both Swords Dance and Dragon Dance for boosting options. Come in on a foe that Crawdaunt scares out (like Hippowdon and G-Corsola) and start dancing. Swords Dance turns Crawdaunt into a monstrous Wallbreaker, able to crack all but the toughest of foes with ease:
+2 252+ Atk Life Orb Adaptability Crawdaunt Knock Off (97.5 BP) vs. 252 HP / 252+ Def Toxapex: 304-359 (100 - 118%) -- guaranteed OHKO
+2 252+ Atk Life Orb Adaptability Crawdaunt Knock Off (97.5 BP) vs. 252 HP / 252+ Def Seismitoad: 494-582 (119.3 - 140.5%) -- guaranteed OHKO
+2 252+ Atk Life Orb Adaptability Crawdaunt Knock Off (97.5 BP) vs. 252 HP / 252+ Def Ferrothorn: 338-400 (96 - 113.6%) -- 75% chance to OHKO
+2 252+ Atk Life Orb Adaptability Crawdaunt Crabhammer vs. 252 HP / 252+ Def Corviknight: 411-484 (102.7 - 121%) -- guaranteed OHKO
+2 252+ Atk Life Orb Adaptability Crawdaunt Crabhammer vs. 252 HP / 0 Def Mandibuzz: 564-665 (133 - 156.8%) -- guaranteed OHKO
+2 252+ Atk Life Orb Adaptability Crawdaunt Knock Off (97.5 BP) vs. 252 HP / 252+ Def Tangrowth: 354-416 (87.6 - 102.9%) -- 18.8% chance to OHKO
+2 252+ Atk Life Orb Adaptability Crawdaunt Crabhammer vs. 252 HP / 200+ Def Kommo-o: 188-222 (53.1 - 62.7%) -- guaranteed 2HKO after Leftovers recovery
Of course this leaves Crawdaunt difficult to use vs Offensive teams, who are often faster and can threaten the OHKO in turn, outside of a Boosted Aqua Jet. Dragon Dance, while not having as drastic a boost in offensive, still makes Crawdaunt plenty threatening, outspeeding up to Neutral nature Base Speed 100 targets and Positive Nature base 92 (speed tie with base 93) when Adamant and outspeed up to neutral nature Base 120 and positive nature Base speed 106 targets when Jolly.
As for offensive moves, Crab Hammer and Knock Off are great STABs, the former possessing insane power and a high crit chance and the latter doubling in power when knocking off an item. Aqua Jet is the preferred final move, getting priority to address Crawdaunt's speed issues. X-Scissor hits opposing Grass and Dark types who resist both of Crawdaunt's STABs, while Close Combat does slightly more damage vs Ferrothorn (guaranteed OHKO after Swords Dance) and Crawdaunt's best option vs Kommo-o.
Checks and Counters
Dragapult -Always outspeeds and can OHKO with STAB or super effective coverage while resisting Aqua Jet. Obviously does not want to switch in cause Adaptability Knock Off is disgusting.
Kommo-o -Resists both of Crawdaunt's STABs, doesn't mind any coverage move, defensive set can take boosted Swords Dance hits comfortably and OHKO with STAB move in turn. (note that Offensive Sets can be overwhelmed after Crawdaunt sets up).
Zeraora -always outspeeds and can OHKO with STAB. Again, does not want to eat a move on the switch in and Swords Dance boosted Aqua Jet will KO 75% (with Jolly Nature)
Azumarill -can eat a hit and OHKO with Play Rough. Does not want to switch in as Crawdaunt nearly 2HKOs unboosted.
Conkeldurr -can OHKO with boosted (Band or Guts) Mach Punch.