Raid script from
https://stevecooktu.github.io/sv_raid_lookup/. 500 seconds/8.3~ minutes is a bit longer than Tyranitar and Salamence's 450 seconds, and a small mercy of this raid is Metagross only has a mere 25x HP multiplier off a relatively weak 80 HP stat and only a 25% shield to break through, which I appreciate gamefreak for considering to make this raid possible compared to how it's set in every other aspect.
Despite not achieving a solo win just yet after a day, I decided I may as well post a preliminary update on Azumarill, because this is looking to be Azumarill's greatest challenge yet (ignoring Mewtwo). But with lots of practice and experience, I am confident that it is possible if not human-viable for Azumarill to do the impossible and bring down the oppressive robot. I have the ideal strategy pretty much down, it's just that the execution is very dependent on NPC team support or Metagross choosing to Earthquake or not.
Here are my best attempts with Arboliva/Arcanine, Arboliva/Drifblim, and Arboliva/Gardevoir, being just about 1 turn away from finishing at red HP, usually thanks to good luck and Metagross giving me free turns with Earthquake or so. Currently I am resetting/grinding for a team comp involving three fully beneficial NPCs instead of only two in order to maintain any advantage I can get, because I felt that if I need near-perfect RNG to succeed with an imperfect team, I may as well go for a near-perfect team as the only thing I can preserve. So far my NPC teams have been one mon short of everyone contributing, so there is still room for improvement in a way that I can actually influence. I have also been working on optimizing the resetting process by recognizing that both the Arboliva NPC and Gardevoir NPC have green hair.
I will have more on Metagross itself and the exact Azumarill execution/gameplan when this actually finishes, but here's what I have settled on so far (similar to the Falinks set posted earlier but outsourcing 50% crits to Lansat Berry), as well as some general notes about the battle that may be of interest.
As you may see, I have gone through a whole rebuild of Azumarill (with multiple iterations), because you can not afford to pull any punches and Azumarill needs every single advantage it can get, burning everything it can in its heart against the soulless machine that is Metagross. Up until this point, I've been satisfied with just tera STAB and a dream, but this fight has pushed me beyond the unwritten limits I've set for myself.
As a preview, the current set is 92 Attack / 252 Defense+ / 164 Speed (suggested by Arcticblast). Azumarill hitting a 177 Speed stat manages to outspeed Metagross by 1 (they tie if both are paralyzed and round down but ideally that shouldn't happen), which helps to set Defense Curl and Rest before it can move which can really save HP overall compared to being slower (unless you have the appropriate support to make up for it). 252 Defense with a positive nature is to try to stay as healthy as possible, as Azumarill needs all the help it can get when it has to take every attack raw with no way around it. 92 Attack is what's left over. (Some screenshots have 342 HP but I reallocated that into Attack later.)
As a note, here is what Azumarill faces on turn 1.
+1 0+ Atk Tera Steel Metagross Meteor Mash vs. 0 HP / 252+ Def Azumarill: 230-272 (67.4 - 79.7%) -- guaranteed 2HKO
Possible damage amounts: (230, 232, 236, 238, 242, 244, 246, 250, 252, 254, 258, 260, 262, 266, 268, 272)
Azumarill can barely avoid Lansat Berry triggering on its first life at a 10/16 chance with damage rolls (25% of 341 HP is 85 rounded down, so anything above 255 damage will trigger Lansat.)
Generally Azumarill will get in a Tera Blast to charge, and then set an offense cheer to die on its first life and preserve both cheers permnanently.
(I have also considered using another Tera Blast instead of a cheer to save a turn of charging as well as having an extra cheer for later, but I believe the damage is just worth it to be able to 5HKO instead of 7HKO with Tera Blast assuming the crits all work out well.)
The second phase (aka the shield/setup/midgame phase) is really played by ear and depends on NPC involvement/Metagross move choices as mentioned, but the goal is to set 2-3 Defense Curls, 2 tera charges, and also Belly Drum. This can end up requiring a cycle of Rest/heal cheers or even eating through sleep turns to save a heal cheer for later in the fight, but with burn or Life Dew support this time pressure can be lightened up. At worst I've had to use Rest to get enough HP to Belly Drum, and then Rest after Belly Drum again just to have enough HP to survive the turn post-buff reset.
This phase is also the point where I discover if Metagross is +2 Attack or not based on how much damage it's doing. After setting up Defense Curl (while outspeeding), Zen Headbutt/Thunder Punch together will do around 90-130 to a +1 Azumarill if Metagross is +2, and at +2 Defense Azumarill faces about 69-102 damage from the combination. +2 Earthquake does ~40 damage in Grassy Terrain against a +1 Azumarill and so Grassy Terrain's 21 HP heal basically makes it a non-issue, and even with Tera Fire Earthquake will do less than everything else while still in Grassy Terrain, though outside of Grassy Terrain it does become Metagross's strongest option. I mention this later but Metagross's move choices seem basically random after it sets up to at least +2 on a turn and stops using Meteor Mash.
You also need to actually get into 25% HP range at this point to set up Lansat Berry, which can be easier said than done if you have too much burn/Life Dew support and defense boosts going on. So sometimes you have to play it by ear and instead of stacking 3 Defense, only go for 2 or get a tera charge in instead. Belly Drum can help here, but with Grassy Terrain involved and Metagross being inconsistent with its move choices, the timing and HP range to survive a hit can be pretty tight to manage. But if I do have Lansat secured, then I like to tera ASAP even if it's just to use Rest, because super effective Earthquake in Grassy Terrain is preferred over super effective Thunder Punches (or Meteor Mash if it's still using that).
After Azumarill is all set up, ideally it will be blasting Metagross with these for a 5HKO. Usually this does not break the shield in one shot (barely falling short) but sometimes it can with some chip. If that happens (or a crit + noncrit breaks the shield) then you can potentially avoid the buff reset and getting attacked in the same turn, and potentially allow the AI to chip Metagross into the buff reset instead allowing Azumarill to set up Defense Curl safely on the free post-shield turn. Otherwise you may usually just end up taking a full powered hit without defense buffs up (unless Metagross is burned) and so want to be healthy before that point.
+6 92 Atk Huge Power Tera Fire Azumarill Atk Cheer Tera Blast (80 BP) vs. 0 HP / 0 Def Tera Steel Metagross on a critical hit: 1662-1956 (22 - 25.9% of 25x hp boss) -- 4.9% chance to 4HKO
After the shield breaks and Metagross resets Azumarill, this is where the plan is less stable but ideally Azumarill can get back to +2 Defense and set Belly Drum back, maybe even Rest and/or heal cheer and hopefully get enough crits and survive and win. This final phase is the most questionable and risky, but is also open to the most potential NPC support with status, as I will go over later.
AI notes:
I have consistently noticed that Metagross seems to see Meteor Mash as a setup threshold move and mostly avoids using it against anyone (until the random double attack phase after 40% HP) after the turn it gets to +2 or above, even with mons like Gardevoir on the field. This provides a fortunate amount of consistency in not using its strongest attack and what kind of damage to expect at minimum, though even against Azumarill it seems to randomly choose one of its other attacks (Thunder Punch/Zen Headbutt/Earthquake), with Earthquake in Grassy Terrain being pretty much a free turn choice.
This conversely means while Metagross is still +1, it seems to prefer Meteor Mash, and may well manage to proc the attack boost against multiple party members in the same turn to get to +3 or even +4 which is pretty much a reset.
Theoretically you can prevent the Iron Defense setup with 2 25% paralysis procs. For Azumarill this would require a turn 1 30% Body Slam paralysis upfront, but assuming that goes through then you would have a 1/16 chance of both Iron Defenses being cancelled and a 6/16 chance of one being cancelled. (1.875% chance overall of Metagross ending up at +0) I tried playing against what was usually a +2 Defense Metagross for a while with Shell Bell/Leftovers for practice early on, but ultimately found it too slow and unwieldy to play around.
I also even tested setting Freeze with Ice Punch to see if I could deal with waiting out the timer and Metagross attempting to use its moves while frozen, which would be a 10% * 80%^5 chance to maintain freeze across the 3 NPC turns and 2 scripted turns (I was running a slower Azumarill at this point so it would not attempt to thaw on my turn), ending up with a cool 3.2768% chance of success in comparison. However it turns out that scripted moves interact with freeze differently than paralysis, and so I waited out the timer but Metagross didn't attempt to do anything. It was only after Metagross actually thawed out when it finally used its queued up Iron Defenses. Well played game freak.
NPC notes:
Clear Body renders a lot of NPCs pretty much useless, and +4 Defense makes some even worse than others. However, some NPCs can still be extremely relevant here, and I will note my experiences here.
Arboliva: As mentioned, Arboliva is a great support for Fire types (though maybe not Earthquake users). Seed Sower into Grassy Terrain provides consistent healing almost all the time, and pretty much cancels out Earthquake's damage potential making it a free turn to set up with. Safeguard can protect against Thunder Punch paralysis and Earth Power is a solid chip damage move.
Gardevoir: Not the most reliable with Life Dew healing timing, but it can come through to save HP/healing turns in both the shield phase and the post-shield phase, which the next few important supports both lack in one area. Synchronize can also potentially paralyze off of Thunder Punch, though it's pretty unlikely and even more unlikely if you combo with Arboliva's Safeguard. Gardevoir is also smart enough to only use Dazzling Gleam instead of ever using Psyshock here.
Arcanine: Arcanine is actually a pretty interesting NPC to grind with. It doesn't press Leer because Intimidate reveals Clear Body, so it consistently goes for Flamethrowers which is relatively good chip damage (perhaps the best of the NPC options) before and after the shield, and has a 10% chance to burn Metagross which the chance of eventually proccing adds up over time and can change everything in making the setup phase more tolerable. Burn's 1/8 HP chip damage is actually relevant too the earlier you get it, even with doing 1/200 of the raid boss's HP a turn, it's still helpful against a shield upfront.
Overall I would say Arcanine can be helpful for setting up in the midgame/shield phase, but may not be as reliable to set burn again after the debuff reset.
Drifblim: Drifblim's Will-O-Wisp allows it to set burn after the shield/debuff reset making it a more consistent lategame support than Arcanine, and potentially active for the scariest part after Metagross removes Azumarill's defense buffs. Drifblim is also a strong sleeper pick for reasons I wasn't expecting.
Due to being immune to Earthquake, Metagross is forced to kill it with contact moves which proc Aftermath, letting Drifblim deal 1/4 of Metagross's base HP or 1/100 (1%) of Metagross's boss HP with every faint. This is also helpful chip damage against the early shield, and to demonstrate how strong this is in practice, I had an Arcanine/Drifblim/Arboliva combo without burn manage to almost break the shield on their own without me actually contributing other than 3 non-tera Tera Blasts to charge tera. Unfortunately this team was lost to a softlock early on, but I didn't really have much practice at that point either.
Umbreon/Dudunsparce: Arboliva/Umbreon/Dudunsparce was the first team I locked in. These guys can help set paralysis with status moves after the shield. Umbreon has better chip damage with special moves/Dark Pulse but a 90% accurate Thunder Wave compared to Dudunsparce's Glare and Drill Run, but Umbreon can also proc Synchronize as well. They will waste some of their turns trying to paralyze against the shield though, unless someone like Arcanine manages to set burn OR you can set your own status somehow like with Body Slam (mentioned above).
Every other NPC mon performs kind of awfully here and only here for chip damage, but Bellibolt and Toxapex can at least hit unresisted on the special side which is better than every other mon being physical or Sylveon. Admittedly I have not played with Bellibolt seriously yet, so I do not know if it tends to spam Mud Shot or Discharge, but perhaps it could also be a source of midgame paralysis and Electromorphosis Charged Discharges if it does, though it will also waste turns on resetting Light Screen.
So that's where I'm at right now, trying to find 3 NPCs that will pull their weight and help make either setup phase more consistent.
Bonus: (This doesn't really fit as part of my final strategy or my best strategies but it was a part of the process.)
After some dissatisfaction with the Body Slam setup early on, I even tried using Flame Orb Fling myself, just to see how setting a burn could improve my setup phase. Despite having no way around the +4 Iron Defenses with my item and 4th move slot both sacrificed, this attempt actually made it past the shield and into yellow HP, being the farthest progress I had ever made with Arboliva/Dudunsparce/Umbreon so far. Part of that might also be because the game just plays out a lot faster without all the Shell Bell/Leftovers healing in comparison, but it incited me to change further. This is what inspired me to fish for early burns with Arcanine and practice with different NPC teams, as well as swapping around my 4th move slot to Rest for healing/utility and instead devoting my item slot to Lansat Berry for raw damage.
tl;dr Azumarill is not done yet but it's not done for.
Jirachi could also use a similar set. Jirachi's Steel type stops Metagross from using Meteor Mash for Attack boosts which should help survivability. Iron Defence in the last slot would be the natural choice for staying alive.
