Cool idea, but yeah the gambit thing is a big problem. You also are incredibly weak to scarf darkrai and moon, who both outspeed you at +1 and are common mons (dark pulse is a 2hit ko even at +1 sp defense). Like, if you have say a dark+fighting+fairy type i.e. anti dark squad, then it could work, but that's an issue. The other two common tera types, ground and dragon, are only weak to one priority type as well. And while hitting most things neutrally is good, it means you can't get the ohkos you want, thus opening yourself up to revenge kills.
+1 252 SpA Tera Ghost Volcarona Tera Blast (80 BP) vs. 0 HP / 4 SpD Heatran: 192-226 (59.4 - 69.9%) -- guaranteed 2HKO after Leftovers recovery
+1 252 SpA Tera Ghost Volcarona Bug Buzz vs. 64 HP / 0 SpD Raging Bolt: 250-295 (61.4 - 72.4%) -- guaranteed 2HKO
Again, could see it working, but tera ground/dragon hits more things super effectively.
This isn't the case for Darkrai. Scarf Darkrai does like less than half to you, and this is even more so if you have the +1 from Quiver Dance. If you Tera Ghost, even Dark Pulse does 82.9 - 98.3% even before the Quiver Dance buff. At +1 it's more like 55.9 - 66.2%. It's a 2HKO even if you Tera Ghost.
Generally, whoever of Moon or Volc is faster/more setup wins barring Tera. Moon has the edge because of Booster Energy and a better speed tier. Volc typically needs to be at + 2 to deal with it. Moon can commonly Tera Flying to resists Bug Buzz, but not all Volc's even run it and then it doesn't resists Fire. So it requires a prediction. This is the case with every Volc set there is.
Gambit is always an issue. I have never heard anybody say that any other Volc set isn't good because Gambit exists. You can also choose when and if to Tera depending on circumstances. You would need to get multiple KOs against the opponent before Sucker Punch 1HKOs in the non Tera form. Like, even Choice Band max attack Adamant Gambit does 88.7 - 104.5% with Sucker Punch before Tera. And this is against a Volcarona that is completely uninvested in defense. Realistically, it won't KO from full even if there are 2 fainted opposing mons and it is using Black Glasses.
This is obviously a different case if you Tera Ghost, but you would be weighing your Tera based on what is happening in the game. If you can counter something like Dragonite, maybe it's worth it to burn a Tera and be vulnerable to Gambit. Or maybe not. I don't think it's that much of a concern.
The only Tera I have seen anyone run that resists Sucker Punch is Tera Fairy. I don't know of anyone who ran Tera Dark or Tera Fighting. Tera Fighting maybe has a shot since it is also super effective to Heatran. But I haven't tested it or run any calcs to know how feasible that is. It also doesn't help at all against Clod. I don't even know of a situation where I would run Tera Dark.
I don't know if Tera Ghost Volc is good. But if it isn't, it won't be because of the Dark types. The
main issue of what you said are Heatran (which is a common check for non-Tera Ground) and Raging Bolt. I feel like being able to 2HKO Heatran is still pretty good considering it is supposed to be a check and you probably out damage it. Raging Bolt with BE would 2HKO with Thunderclap, which is a real issue if you are also 2HKOing it. Now you lose to 2 of the 4 most common priority at +1.
Havent really played a lot lately but loaded up a couple of matches and tried out some fun sets.
I have been using this set to lure in Volcs
DK Crew (Rillaboom) @ Terrain Extender
Ability: Grassy Surge
Tera Type: Fire
EVs: 80 HP / 252 Atk / 176 Spe
Adamant Nature
- Swords Dance
- Grassy Glide
- Tera Blast
- High Horsepower
Vol users will think of Rilla as free switch in, since the standard sets usually are. You set up with DK on a mon that is usually threatend out by it like Prim and then Tera fire and Volc will become a set-up fodder. Also lures and takes care of the metal birds, CS Kyurem, Heatran and even Gouge although you gotta tera at the right time against BS GF.
Pairs nicely with the Goobfather Gambit who appreciates the above mons being gone.
I really like this. Grass and Fire is a nice attacking combo. There was discussion on Tera Fire Meow earlier mostly to avoid burns, but fitting Fire TB on Rillaboom seems a lot better. This is a cool idea.