I
guessed that
Falinks would work with extra damage from the double STAB after it gets tera, compared to other Body Press users like Orthworm and Corviknight who only get single STAB. Having Metagross go for the immediate, unremovable Hone Claws puts a snag in that, but it does work in this raid after all.
Instead of boosting up with Iron Defense right away, the first turn should be a
Body Press just to build tera charge. Zen Headbutt does a maximum of 314 damage to a max-defense build, so it can't possibly OHKO (you are using Battle Armor, right?), but will leave you at guaranteed low health (the one good thing about Hone Claws is it eliminates the miss chance so the logic of the first couple turns is consistent). That sets you up for the permanent defense cheer, with the respawn timer overlapping with the first of the Iron Defenses that get triggered on the timer drain. Now with that cheer in hand, further Zen Headbutts do low enough damage* that you can build up all three of your own
Iron Defenses, and a
Focus Energy, and the second and third Body Presses with their corresponding Shell Bell recovery, all before HP becomes an issue.
* - Take note of the teammates you get, and what moves Metagross is likely to use against each one. If you get some that draw Meteor Mash, like Garganacl or Weavile, every turn is just giving them extra chances to get more than the one unremovable attack boost. Gardevoir is in the same category, though it does at least sometimes provide heals to offset this. Check the boss's stat boosts periodically if you see these teammates, as if it ever gets to +2 attack or higher, the reset is probably unrecoverable. Or if you don't like the odds, simply reset right away until you don't have those teammates.
Once the tera charge is filled up, you'll probably be in red health, so use the last move--
Rest--and immediately follow up with a heal cheer to get back into action after missing only one turn. Because of Metagross's (once again unremovable) +4 defense, critical hits (which happen 50% of the time after Focus Energy) deal 4.5 times as much damage as non-criticals. You might get a non-critical immediately after going tera, which probably won't break the shield. Rather, whenever the critical does come, that'll blow clear through the shield and the trigger for Metagross's wipes. After your Shell Bell recovery back to full on this hit, you have to take one Zen Headbutt with +0 defense, though at least you have the permanent heal cheer so it won't come quite as close to the KO as turn 1 did (unless of course it's fished for Meteor Mash boosts along the way).
The good news is that after a shield break, Metagross will skip its move on the next turn that starts after that point, so you can build back up to +2 without facing immediate retaliation. The bad news is that you might not have enough HP left to survive if you just boost to +4 against on the turn after the freebie. Instead, the key is to go for a double-STAB Body Press at this point, but you must get the 50% critical on this exact turn in order to get back enough Shell Bell recovery to survive. Otherwise it's a reset.
If you did get that critical, the rest is easy. You'll have enough of a buffer to boost back to +6, then a couple more Body Presses should be enough, as long as they include at least one more critical.
Zapdos @ Shell Bell
Malamar @ Covert Cloak (or something else)
