Torterra is pretty scary in an absurd way, so here's an Azurill solo clear for what may be its last hurrah for now. It was both more and less viable than I expected in some ways, but overall it took longer than expected, mostly because I saw the path to victory very early on but Torterra kept denying it. At this point I'm just putting my notes together off the cuff so some points may seem redundant.
Fails
Here is Torterra releasing its energy right after I input my final hit despite the timer and being basically dead.
Here is Torterra killing me with a double attack Earth Power despite being basically dead.
Here's Torterra running out the clock again before the final hit despite the timer.
Moves and Stats
Azurill mostly follows Azumarill's example and strategy, though it only has Waterfall/Tera Blast as Water STAB (the former is probably faster to animate and better if you die post-tera/shield though I didn't run into that) and isn't naturally found as a Water tera, and doesn't have Rain Dance in its levelup learnset.
Azurill can afford to run Huge Power over Sap Sipper since Earthquake generally does more than Wood Hammer thanks to being Normal type, though as I'll go into later, it needs multiple Intimidate NPCs and Azumarill could honestly do something similar with the same support.
The most important thing about this fight is being able to take a hit to set Mud-Slap, which Azurill is not great at. For a while I just left myself with 252 HP but I faced a notable chance of getting OHKOed turn 1 from Earth Power:
+2 0 SpA Tera Ground Torterra Earth Power vs. 252 HP / 4 SpD Eviolite Tera Water Azurill: 274-324 (90.1 - 106.5%) -- 43.8% chance to OHKO
This also affects some other instances like +4 Torterra vs defense cheer preserved Azurill (x2 SpA vs base Azurill is equivalent to x3 SpA vs 1.5x SpD cheered Azurill), or +2 Torterra critting a defense cheered Azurill, but surviving turn 1 to at least get the defense cheer off was key to an attempt going through and it didn't feel great to fail immediately after watching Shell Smash's buff messages every time. You could set the defense cheer yourself but it feels like a waste and having the option of a heal cheer later is also valuable.
In the end, Azurill can guarantee surviving both Earthquake and Earth Power T1 with 2 Intimidate NPCs and specific EVs, as well as the Eviolite boost. I didn't want to rearrange my EVs but it was probably worth it just for this specific thing.
Mutually, preserving a defense cheer is also necessary to survive +4 Earth Powers later as mentioned, and at that point you may as well set an offense cheer as well for damage. Sometimes Torterra opens with Smack Down as well but not that often.
0+ Atk Tera Ground Torterra Earthquake vs. 0 HP / 64 Def Eviolite Tera Water Azurill: 204-240 (84.6 - 99.5%) -- guaranteed 2HKO
+2 0 SpA Tera Ground Torterra Earth Power vs. 0 HP / 168 SpD Eviolite Tera Water Azurill: 204-240 (84.6 - 99.5%) -- guaranteed 2HKO
Aside (Marill vs. Azurill, calcs)
For anyone wondering about Marill, I think Marill and Azurill should theoretically perform very similarly in this raid, with some minor differences I will cover here. Generally I just didn’t want to go through this again and build a new physical tera Water Sap Sipper Marill when I could use my existing Huge Power Azurill.
Defense
Regarding turn 1 survival, Marill is naturally weak to Grass and does face the chance of a turn 1 non-critical OHKO unlike Azurill without sacrificing Attack investment. Marill can run Sap Sipper to simply counter this and any random Wood Hammers, but the free turn at the start doesn’t add much since you die, compared to Huge Power halving the time needed in the raid.
Like Azurill, Marill is threatened by an overkill OHKO from +2 Wood Hammer both on Turn 1 and after the second Shell Smash with a defense cheer set, so 2 Intimidate NPCs are still necessary for it to survive. Torterra might choose Smack Down either way though based on Azurill.
0+ Atk Tera Ground Torterra Wood Hammer vs. 0 HP / 252 Def Eviolite Tera Water Marill: 242-288 (86.1 - 102.4%) -- 18.8% chance to OHKO
On the other hand, Marill can always take an Earth Power from full health naturally with no HP or SpD investment.
+2 0 SpA Tera Ground Torterra Earth Power vs. 0 HP / 0 SpD Eviolite Tera Water Marill: 236-278 (83.9 - 98.9%) -- guaranteed 2HKO
With Intimidate support, Wood Hammer’s damage can be mitigated in the long run and Marill will end up in the same position as Azurill. On the other hand, Marill can run Sap Sipper to simply ignore this and any random Wood Hammers, but I think Huge Power is better overall just to halve the time of the raid since the free turn at the start doesn't impact much.
Offense
As mentioned, Azurill’s best physical Water moves are the 80 BP Tera Blast/Waterfall, both which are TM moves. I guess Waterfall can be better if you keep a run going and die but still have remaining time, it also might animate faster but I haven’t timed it.
On the other hand, Marill has access to the better 85 BP Liquidation that can lower Defense and a matching Water tera type for 2x STAB, but it needs Huge Power to surpass Azurill’s damage output with all other things equal. Still, it's pretty respectable.
+6 252+ Atk Huge Power Tera Water Azurill Atk Cheer Tera Blast (80 BP) vs. -1 0 HP / 0 Def Tera Ground Torterra in Rain: 2862-3368 (24.7 - 29% of 35x hp boss) -- 99.9% chance to 4HKO
+6 252+ Atk Tera Water Marill Atk Cheer Liquidation vs. -1 0 HP / 0 Def Tera Ground Torterra in Rain: 2032-2392 (17.5 - 20.6% of 35x hp boss) -- possible 5HKO
+6 252+ Atk Huge Power Tera Water Marill Atk Cheer Liquidation vs. -1 0 HP / 0 Def Tera Ground Torterra in Rain: 4056-4776 (35 - 41.2% of 35x hp boss) -- guaranteed 3HKO
Strategy
Azurill pretty much has to do the same thing as Azumarill, but riskier because you don't get the insurance of taking a hit with Shell Bell healing among other things.
Firstly you still have to die early, generally by using a move T1 and an offense cheer T2 to faint with both cheers up and permanently preserved. You still have to live turn 1 for the AI to get a turn and set the defense cheer, which is why defense investment is still relevant. As mentioned earlier, I considered you could just press defense cheer turn 1 as well instead of letting the AI do it but then you lose a potential heal cheer for later. As mentioned, Azurill needs 2 Intimidates to survive T1 Earthquake and make it more manageable in the long run which was what I locked in for.
Generally I just pressed Belly Drum on turn 1, usually it fails but if Torterra Smack Downs then you just cut your HP a bit. You can attack Torterra or your ally with Mud-Slap/Tera Blast if you want chip damage/tera charge, but it doesn't really matter to me because I just go for 3 accuracy drops anyway and I like to keep my PP counts separate to remember what I used them for. If anything, hitting Torterra with Mud-Slap can backfire if it just doesn't kill you and the cheer wears off.
Input speed or dying too slow at the beginning because of Intimidate/Smack Down doesn't matter too much because after you die, you have the bottleneck of waiting for Torterra to debuff reset. It seems reliable to sneak in a Mud-Slap before the Shell Smash because it lets you take less damage which can save you HP to heal if you get lucky with dodges or a light Smack Down, and taking another move lets the Intimidate AI potentially die and respawn. Also if Torterra crits in that scenario then you can live it with the defense cheer.
(This is a random image of such a failed attempt just to show how much time you could work with on a 3rd death.)
Afterwards things get tricky because you kind of have 2.5 lives to play with at this point. I say this because Azurill can kind of afford to just eat an Earth Power and trade with Mud-Slap even if you don't dodge, and it can do it again for the 3rd life (15s respawn) with a reasonable time. But you only really have time for a last round if you die ASAP in the first ones, so if something happens like Torterra chips Azurill and starts missing and then you pivot to heal cheering and then it hits again then there's not enough time.
Torterra using the scripted Earthquake actually wastes a lot of time with either 4 potential miss messages or the animation just playing out normally, and as shown the timer is less than it seems. The most reliable indicator seems to be the tremendous energy/10% time remaining, but even then it can be delayed by another animation.
A viable run for me at this point was getting to -3/-4 accuracy, ideally letting you go into the 3rd/4th life with full HP and just setting up from there. Generally this just involved getting 1 dodge since Azurill is guaranteed to survive 2 lives and hit 2 Mud-Slaps unless it gets crit. I would generally just press Mud-Slap if I was at low HP, and if I was still alive by -4 accuracy then I would go for the heal cheers.
After you're comfortable with accuracy drops and health from healing or dying, Azurill just has to set Belly Drum, Rain Dance, and hope not to die to Earth Power, or die and respawn if you can still afford the time. Earth Power is a guaranteed kill at this point but Torterra using a physical move can be survivable if the Intimidators have been dying often. I think rain is still pretty helpful to speed things up especially with usually so little time left.
Water Tera Blast is about a 2HKO on the shield and should be close to a 4HKO overall, though I ended up seeing it barely 5HKO a few times as shown above which I can only attribute to shield reduction, damage rolls, and AI chip. There is no chance of a helpful crit thanks to Shell Armor.
After those 2 turns of setup you should face about 3 more hits from Torterra (free turn after the shield breaks), plus potential double attacks, and the scripted spread Earthquake that doesn't hurt that much after Intimidate has taken its toll but still depends on remaining health. Just after reaching that point, the base chance of dodging those 5 hits at like -3 accuracy is 1/32.
Successful run
I ended up pressing Mud-Slap on Torterra turn 1 accidentally (still went for 3 so it didn't matter), and took 3 deaths in the end. Life 2 was a typical Mud-Slap into death next turn, and life 3 started with a miss, and then a hit where Earthquake did not take me below half HP, reaching my target of 3 Mud-Slaps, but I died the next turn anyway. Then on life 4 I just sent it on the setup and mashed Tera Blast, the tremendous energy message happened right after the shield going down.
Overall while frustrating to see through, this wasn't too bad to execute and was an interesting challenge to figure out. It goes to show how you can burn a lot of different resources in raids like HP and time, as long as you can make the opportunity to do so in the first place and don't run out. I don't think cheer preservation on death has any part in gamefreak's intent with these raids, but it happens to work out as a nice risk/reward mechanic and also saves time waiting for timed actions.