Crobat with 30i spread used in calc for obvious reasons
Pokemon that are able to RK 30i:
252 SpA Tapu Koko Volt Switch vs. 0 HP / 0 SpD Crobat in Electric Terrain: 314-372 (100.9 - 119.6%) -- guaranteed OHKO
252 SpA Tapu Koko Thunderbolt vs. 0 HP / 0 SpD Crobat: 312-368 (100.3 - 118.3%) -- guaranteed OHKO
Koko is able to KO with Thunderbolt even when Electric Terrain is not active: otherwise, Volt Switch is just as capable at OHKOing 30i
252 Atk Syclant Icicle Crash vs. 0 HP / 0 Def Crobat: 278-330 (89.3 - 106.1%) -- 37.5% chance to OHKO
Even without Choice Band you have a roll to KO. Weavile performs similarly, if not better due to running Triple Axel.
252 SpA Choice Specs Dragapult Shadow Ball vs. 0 HP / 0 SpD Crobat: 217-256 (69.7 - 82.3%) -- 56.3% chance to OHKO after Stealth Rock
252 SpA Choice Specs Dragapult Draco Meteor vs. 0 HP / 0 SpD Crobat: 351-414 (112.8 - 133.1%) -- guaranteed OHKO
Draco can KO you while Shadow Ball has a good roll after taking Rocks damage.
252 SpA Tapu Lele Psychic vs. 0 HP / 0 SpD Crobat: 390-462 (125.4 - 148.5%) -- guaranteed OHKO
Scarf Psychic has no trouble KOing you, considering this is the strongest attacker on here.
252 Atk Zeraora Plasma Fists vs. 0 HP / 0 Def Crobat: 320-378 (102.8 - 121.5%) -- guaranteed OHKO
4- SpA Zeraora Volt Switch vs. 0 HP / 0 SpD Crobat: 186-218 (59.8 - 70%) -- guaranteed 2HKO
Low investment Volt Switch is able to 2HKO you, giving Zera a bit more room in its ability to threaten or force you out, though you will not fall to Stealth Rock + Volt Switch.
Zera can opt for a -Def/SpDef nature if it wants to preserve damage for Special Attacks. In this case you can fall from Rocks chip + Volt Switch. Max SpA sets only secure an OHKO if Rocks are up.
4 SpA Zeraora Volt Switch vs. 0 HP / 0 SpD Crobat: 204-242 (65.5 - 77.8%) -- 25% chance to OHKO after Stealth Rock
252 SpA Zeraora Volt Switch vs. 0 HP / 0 SpD Crobat: 258-306 (82.9 - 98.3%) -- guaranteed OHKO after Stealth Rock
252 SpA Tornadus-Therian Hurricane vs. 0 HP / 0 SpD Crobat: 211-250 (67.8 - 80.3%) -- 43.8% chance to OHKO after Stealth Rock
Torn is the weakest offensive answer on here so far, as Hurricane only has a chance to KO even with Rocks up, and it has to hit Hurricane. Still, this is a pressure matchup and staying in on a potential Hurricane is a risk you have to be willing to take.
The list of answers is greatly increased if you choose to run Adamant. Of note:
252 Atk Choice Band Urshifu-Rapid-Strike Surging Strikes (3 hits) vs. 0 HP / 0 Def Crobat on a critical hit: 300-354 (96.4 - 113.8%) -- guaranteed OHKO after Stealth Rock
252 SpA Life Orb Krilowatt Thunderbolt vs. 0 HP / 0 SpD Crobat: 374-445 (120.2 - 143%) -- guaranteed OHKO
30is switch-ins:
0 Atk Landorus-Therian Knock Off vs. 0 HP / 0 Def Crobat: 70-83 (22.5 - 26.6%) -- 26.6% chance to 3HKO after Stealth Rock
252 Atk Landorus-Therian Knock Off vs. 0 HP / 0 Def Crobat: 84-99 (27 - 31.8%) -- guaranteed 3HKO after Stealth Rock
0 Atk Arghonaut Knock Off vs. 0 HP / 0 Def Crobat: 56-66 (18 - 21.2%) -- 93.1% chance to 4HKO after Stealth Rock
0 SpA Clefable Moonblast vs. 0 HP / 0 SpD Crobat: 65-77 (20.9 - 24.7%) -- guaranteed 4HKO after Stealth Rock
Of note: You can switch into Rocks twice and still dodge a 3HKO from Clef's moonblast.
This one is a bit tricky. If Jumbao somehow gets Traced Tinted Lens you are not in a good position.
252+ SpA Tinted Lens Jumbao Moonblast vs. 0 HP / 0 SpD Crobat: 218-258 (70 - 82.9%) -- 62.5% chance to OHKO after Stealth Rock
Otherwise Scarf Jumbao can only 2HKO you with Moonblast if Rocks are up.
252+ SpA Jumbao Moonblast vs. 0 HP / 0 SpD Crobat: 109-129 (35 - 41.4%) -- 64.8% chance to 2HKO after Stealth Rock
252+ Atk Choice Band Rillaboom Knock Off vs. 0 HP / 0 Def Crobat: 123-145 (39.5 - 46.6%) -- guaranteed 2HKO after Stealth Rock
252+ Atk Choice Band Rillaboom Grassy Glide vs. 0 HP / 0 Def Crobat in Grassy Terrain: 64-76 (20.5 - 24.4%) -- guaranteed 4HKO after Stealth Rock
0 Atk Colossoil Knock Off vs. 0 HP / 0 Def Crobat: 91-108 (29.2 - 34.7%) -- guaranteed 3HKO after Stealth Rock
0 Atk Guts Colossoil Knock Off vs. 0 HP / 0 Def Crobat: 135-160 (43.4 - 51.4%) -- guaranteed 2HKO after Stealth Rock
Admittedly you have a small number of truly safe switch-ins but I think that's a fair trade-off considering what we have going here. Plenty of strong breakers and attackers often need support to get in safely, and I don't see why 30i should be much different.