I have a suggestion about Basculin's Tera typing.
For those unaware, Adaptability only increases the STAB boost to a mon's current typing. This means that :
- Pre-Tera, Basculin gets a 2x BP boost to Water moves thanks to its Water typing and Adaptability, increase the effective base power of its Wave Crash from 120 to 240.
- If Basculin Teras to Water, this boost is further increased to x2.25, further increasing the BP of Wave Crash to 270.
- If Basculin Teras to a different type however, even though it retains the STAB boost from its original typing, Adaptability only applies to its new type, dropping Wave Crash's BP to "only" 180.
- In turn, Adaptability applying to its new typing means it could increase its Tera Blast BP to 160, or its Head Smash to a whopping 300.
With that out of the way, Basculin's only Tera type in randbats seems to be Water. While increasing Wave Crash's damage is nice, I think that Basc could benefit from more versatility, instead of "winmore"-ing its Wave Crash, which already deals immense damage. Some suggestions :
- Dragon and Grass Teras both give Basculin resistances to Grass and Water, its two only weaknesses, which can avoid a crucial revenge kill from Regieleki, Electrode, Meowscarada, or various Scarfers, and KO them with Wave Crash, Tera Blast, or Head Smash.
- Dragon Tera Blast gives Basculin a great option to fight Dragons, particularly Koraidon, which resists both Wave Crash (+ sunlight) and Head Smash. Tatsurigi is also a great target for a Dragon Tera Blast due to its Water immunity and since it is not OHKO'd by Head Smash (barely, admitedly, but Head Smash's low accuracy + an OHKO that is only guaranteed with prior damage makes Dragon Tera much more attractive)
- Grass Tera Blast gives Basculin a reliable way to defeat Gastrodon and Quagsire, which may be immune to Water moves, resist Head Smash, and take low damage from Psychic Fangs and Crunch.
- Some calcs that assume Basc has Tera'd to Dragon, which show that Wave Crash still deals immense damage without its Adaptability Boost :
- Lvl 86 84 Atk Choice Band Adaptability Tera Dragon Basculin Wave Crash vs. Lvl 80 84 HP / 84 Def Regieleki: 317-374 (122.3 - 144.4%) -- guaranteed OHKO
- Lvl 86 84 Atk Choice Band Adaptability Tera Dragon Basculin Wave Crash vs. Lvl 88 84 HP / 84 Def Electrode: 231-273 (92.7 - 109.6%) -- 56.3% chance to OHKO
- Lvl 86 84 Atk Choice Band Adaptability Tera Dragon Basculin Tera Blast vs. Lvl 80 84 HP / 84 Def Meowscarada: 170-201 (67.1 - 79.4%) -- guaranteed 2HKO
- Lvl 86 84 Atk Choice Band Adaptability Tera Dragon Basculin Tera Blast vs. Lvl 80 84 HP / 84 Def Baxcalibur: 276-328 (87.6 - 104.1%) -- 25% chance to OHKO
- Lvl 86 84 Atk Choice Band Adaptability Tera Dragon Basculin Tera Blast vs. Lvl 72 84 HP / 84 Def Koraidon: 256-304 (97.3 - 115.5%) -- 81.3% chance to OHKO
- Another option is Tera Rock. While not bringing any valuable defensive utilty to Basculin, it allows it to circumvent Water-resistant mons like the aforementioned Grass- and Dragon-types
- Lvl 86 84 Atk Choice Band Adaptability Tera Rock Basculin Head Smash vs. Lvl 80 84 HP / 84 Def Meowscarada: 317-373 (125.2 - 147.4%) -- guaranteed OHKO
- Lvl 86 84 Atk Choice Band Adaptability Tera Rock Basculin Head Smash vs. Lvl 82 84 HP / 84 Def Tatsugiri: 343-404 (139.4 - 164.2%) -- guaranteed OHKO
All things considered, my pick would be Dragon > Grass > Rock > Water, but all four could be added to its Tera pool. I'm not sure Tera Water grants Basc any additional kills that it wouldn't already have access to, and in general seems like a bit of a waste of one's Tera button, but I maybe someone can correct me.