Pokemon Violet - 5* shiny Chi-Yu (1) with Araquanid, Dachsbun, and Milotic
0It's the final Treasures of Ruin shiny raid! And isn't a total pushover.
5* (level 75, IVs of 31/20/31/31/31/31) Modest tera fire Chi-Yu (with a whopping x35 HP to compensate for low base HP, and usual 300 seconds) has regular moves Flamethrower, Heat Wave, Dark Pulse, and Snarl. It again immediately starts with Ruination, and at 93% time/HP remaining puts up shield (covering 30% of max HP). At 85% time remaining it steals a tera orb charge, at 75% time wipes player buffs, and at 50% time uses Ruination again; meanwhile, at 55% HP remaining it wipes player buffs again, and at 40% HP it wipes its own debuffs and also starts using a second move per turn 50% of the time. Nothing tricky here.
The main thing that makes Chi-Yu not a pushover is that unlike the earlier ice/grass/ground raids there's no lifedrain move that's super-effective against fire, lol. (You could probably still use a neutral lifedrain move, like Drain Punch spam with Thick Fat Hariyama/Iron Hands/Defiant Annihilape or whatever, though.)
0:00 - Araquanid
Araquanid has crazy SpD, and while it's initially neutral to fire it has Water Bubble to halve fire damage and also boost your water damage, which is quite nice. If that's still no safe enough (which it might not be, Araquanid is so slow that you need a +Spe nature and 172 EVs in order to outspeed, so the 3/40 flinch chance each turn from Dark Pulse's 30% chance can really mess things up) then you can use Skitter Smack to debuff and Entrainment to remove Beads of Ruin's x0.75 SpD... and Rain Dance for another fire-weakening/water-boosting support move.
Apart from that, Araquanid doesn't really have much else, though... Nothing to debuff defense, nothing to boost attack. Spamming Liquidation and hoping for the 20% chance at -1 Def is about all you can do... and like, that's certainly enough to clear the raid as you can see, but it's just kind of a baseline okay run.
For what it's worth, while Belly Drum Azumarill would normally be a shoe-in, the early buffwipe plus earlier shield kinda neuter it; if you just wait to Belly Drum until the buffwipe then the shield's basically almost broken, so it's not really that different from an Araquanid-spamming-Liquidation run. At least it does get Tail Whip to debuff before shield... (I also tried for an Ursaluna oneshot, but unfortunately the shield goes up too early... and also the x35 HP was more than expected and it wouldn't have oneshot anyways.)
By the way, in multiplayer Araquanid is a great team player. Rain Dance to reapply rain after Kyogre's Drizzle runs out, Entrainment to give your allies Water Bubble too...
4:42 - Dachsbun
Chi-Yu's random-move AI has a 50% chance to use a fire move and it has lower physical defense, so here's a Well-Baked Body Dachsbun run with Body Press! Its fairy typing resists dark too (and you continue to resist it after you tera-fighting), so it's pretty safe. You can Tail Whip before the shield, too!
...Unfortunately, as you can see it's super inconsistent. Chi-Yu only used two fire moves across the entire raid! (Once before the first buffwipe, once after the second.) The fact that this was still only maybe one turn slower than Araquanid just goes to show how unimpressive that one was.
9:51 - Milotic
Snarl's real annoying, so why not flip it by using Competitive? Empoleon's another water attacker with it, by the way.
Sadly it's even more inconsistent, unsurprisingly given that you're only dealing with a 1/4 chance for Snarl to be used each turn. (If anything, this is a lucky run because I got Snarled three times.) You can still Rain Dance, and I brought Draining Kiss in order to heal up after getting a bunch of SpA buffs (while otherwise using Metronome Surf)... but in the end I just swapped to a Shell Bell and got this as-slow-as-Dachsbun clear.
For some reason this raid not being trivial inspired me to do a bunch of runs, so expect a second video with my actual preferred counter!