Pokemon Violet - 7* Garchomp the Unrivaled with Bellossom, Sinistcha, and Serperior
2Another mighty pseudo-legend! And this one's nice and straightforward.
7* tera ground Jolly, Rough Skin Garchomp (with x25 HP and a 570-second timer) immediately starts with Breaking Swipe, and then its regular moveset is Earthquake, Poison Jab, Liquidation, and Fire Fang. Very soon after, at 95% HP or 90% time remaining, it puts up shield (covering 30% of max HP); at 76% time it wipes debuffs then immediately follows up with Swords Dance, and uses Swords Dance again at 55% time remaining, whereas at 60% HP it wipes player buffs and at 40% HP it wipes its own debuffs again (and starts using a second move 50% of the time).
...Why Liquidation? The main stuff that resists all of ground/poison/fire are, uh, rock/flying (and I guess Flygon). What weird coverage.
Anyways, early shield is annoying but it's not as bad as the instant-shield from 7* Metagross. No, here the threat is the double-whammy of the debuff wipe followed immediately by Swords Dance, as well as (if you resist everything else) the near-guaranteed poison from Poison Jab's 30% proc rate doing percentage damage.
Intimidate is very useful here! I rolled only Arcanine but its ground weakness certainly makes it the best option; I settled for it because it also came with Haxorus, whose Scary Face would help outspeed Jolly Garchomp.
0:00 - Bellossom
Yet again, we have a tera ground raid where I really wanted to use Bellossom's unique niche of 'can Acid Spray then metronome STAB Giga Drain, but isn't a poison type itself'... and just like 7* Torterra, the raid timings work out such that I never end up using Acid Spray.
Bah!
I was using Charm early on, but found that Strength Sap's healing was more useful (especially with Arcanine picking up the slack with Intimidate). Amusingly, Quiver Dance's speed buff is actually kinda important here: +2 Spe allows Bellossom to outspeed +0 Garchomp (such as right after the debuff wipe), and by the time your buffs are wiped the shield should be down and Haxorus can debuff speed again.
Maybe the one Quiver Dance I use after buffs are wiped would've been better as an Acid Spray... but the second debuff wipe would've reset it anyways. Ah well.
8:39 - Sinistcha
This is very clearly the true counter to this raid.
Grass/ghost already resists ground/water and is neutral to poison, and Heatproof makes you neutral to fire, meaning resisted Earthquake is Garchomp's best option and so you avoid any pesky move side-effects [until you terastallize]. On top of that, Sinistcha can Iron Defense and Nasty Plot, and then attack+heal+burn all in one with Matcha Gotcha! Wow. For consistency you can hold a Wide Lens (as I do here) to raise its accuracy to 99%, but on average a Metronome's ramping damage boost would be optimal, probably.
This was my very first attempt! I didn't actually realize ghost resisted poison, and so I went for the first-turn Strength Sap here... so you could probably just skip that. (You could Grassy Terrain or Reflect or something instead, I guess.)
16:07 - Serperior
Rounding out the set of counters people immediately thought of, Contrary Serperior can mostly blaze through this raid with Leaf Storm into Giga Drain spam. Fun.
Typically I praise Contrary Lurantis for raids since it has marginally better special attack, but in this case Serperior's probably better: using Reflect to halve physical damage for five turns is probably better than using Superpower once or twice, and Serperior's great base speed allows it to outspeed Jolly Garchomp even if it's Modest with a mere 12 Spe EVs. I was getting tired of poison ruining runs so I use a Covert Cloak.
Unfortunately, barely outspeeding it means that Serperior can't really use Scale Shot for +1 Def/-1 Spe, and its selection of moves for the 4th slot aren't much better. Glare can paralyze at the start but the shield goes up so early that it does nothing; Gastro Acid can remove Rough Skin mostly just to remove the ability notification spam but that's pointless; Synthesis can heal but a +2 SpA Giga Drain already full-heals you. I really wanted to be cheeky and use Coil (for +1 Def/accuracy) when your buffs are wiped and your ability is negated for one turn, but for some reason breaking shield plus activating the buffwipe with my own move, then using Coil the very next turn, still had Contrary reverse the buffs. Very weird.
In the end, instead of just not using a fourth move, I decided to pack Sweet Scent in order to make Leaf Storm 100% accurate. How niche.
Other things that have cleared this include Malamar (usual strats), Slowbro (tera water? maybe Stored Power too), Orthworm (Body Press), probably even Dondozo (tera water Liquidation?)...
Before release I saw some talk of Araquanid, and Garchomp doesn't have rock coverage so it might actually work, but unfortunately it can't buff attack stats or debuff defense stats (though at least it has Iron Defense and can debuff attack stats). Might be funny if a Power Split run won somehow...