Pokemon Violet - 7* Serperior the Unrivaled with Delphox and Skeledirge
0Every starter raid has had its hidden ability, and Contrary Serperior heavily restricts what moves it wants to use... and despite its minuscule coverage it has access to a lot of annoying support moves, so this raid more or less came down to what support move(s) it got and whether they were main-moveset or merely scripted.
Turns out they picked the most interesting/annoying option!
Tera grass Contrary Serperior (with x30 HP in a 10-minute raid) immediately leads with... Sweet Scent, a spread -2 evasion move (i.e. it gets x5/3 accuracy). Its regular moveset is then Leaf Storm (-2 SpA special grass), Dragon Pulse (special dragon), Iron Tail (physical steel; no easy win for Sap Sipper Azumarill!), and... Gastro Acid, which negates your ability. At 85% time remaining it wipes player buffs, then soon after uses Breaking Swipe, and steals a Tera Orb charge at 75% time and also puts up shield (covering 60% of the health bar) at 75% time or 75% HP remaining; meanwhile, at 60% HP remaining it wipes its own debuffs, and at 40% it uses Glare. Finally, as usual, below 50% HP it uses a second move per turn 50% of the time.
The main threat is clearly Contrary reversing Leaf Storm's debuffs to reach +6 SpA. A few abilities can handle it (such as Unaware ignoring buffs, or Neutralizing Gas negating abilities, or Sap Sipper countering Leaf Storm), and you can Skill Swap to get Contrary and make use of it yourself... but Gastro Acid counters any strats that rely on your ability unless you hold an Ability Shield to prevent your ability from being cancelled (including by the buff wipe!). Unfortunately, that means no Shell Bell for sustain! What a pain.
0:00 - Delphox
This is a fun pick. Skill Swap removes Contrary, and Delphox can even make use of it by using Overheat (and also reverse Iron Tail's defense debuffs!), and then once you're at +6 SpA you can just swap to Flamethrower/Mystical Fire for accuracy. Timid Delphox can outspeed with no extra speed investment, which is nice.
For whatever reason I decided to hold a metronome instead of a shell bell, which meant healing with Wish... It went okay, as you can see, but shell bell would probably be better. Furthermore, with a moveslot freed up you can pack Nasty Plot or Calm Mind just in case Gastro Acid cancels your Contrary before you're done buffing.
7:02 - Skeledirge
Unaware ignores buffs, and you can hold an Ability Shield to block Gastro Acid and then be forced to heal with Slack Off instead of relying on Shell Bell. Nothing special here.
There are other strats, of course. A few moves can get rid of enemy abilities: the aforementioned Skill Swap, Gastro Acid removes the ability, Worry Seed replaces it with Insomnia, Simple Beam replaces it with Simple, Entrainment replaces it with your own ability...
For example, Galarian Slowking can Skill Swap then Acid Spray (and then go for a Stored Power oneshot?), Victreebel can Gastro Acid and then Acid Spray and Sludge Wave, Venomoth can Skill Swap then Quiver Dance and Acid Spray/Sludge Wave... A whole bunch of good poison options here. (I unfortunately prepped a Galarian Weezing, who's weak to Iron Tail, and I don't want to re-breed a regular Weezing to show off Neutralizing Gas... Oh well.)
I really wanted to use Slither Wing for Leech Life bug attacks, but it doesn't have a way to remove an ability, and despite being able to survive a +6 Leaf Storm and then heal back to full with metronome Leech Life, you do need to Bulk Up in order to counter the Breaking Swipe attack debuff, and also attack early in order to terastallize by shield going up, while also building up metronome... It just didn't want to work out, alas. Plenty of other bugs get it too, but they're all either special attackers (like Frosmoth or Volcarona) or else are so frail that I'd feel uncomfortable using them (like Kricketune or Spidops)...
Maybe you could even simply forget about dealing with Contrary and simply use someone specially-bulky with Amnesia, like Volcarona. Iunno. Plenty of options here.