I completely agree with Electrolyte, we need to choose a strategy right now. I'm not really persuaded Regular Offense is a losing pick here, as long as it's tailor-made to beat their team. For sure I don't like the Stall idea. Thundurus can, and in fact will, break down most dedicated walls, and Meloetta is not easy to handle, either.
Starmie is a really interesting suggestion (and it's one of my favourite pokemons, to be honest), as it can 2HKO everything in their team and OHKO Thundurus with Ice Beam after SR or 1 round of LO recoil, which is invaluable to stop its sweep. However, it cannot literally switch into anything: Meloetta OHKOs with Thunder even in Pirouette forme, Metagross has a 50% chance to OHKO with EQ after Rocks, and still 2HKOs with any move not called Bullet Punch, and Thudurus...well, I don't need to explain. Starmie, on the other hand, needs Rain and Life Orb to OHKO Metagross with Hydro Pump, and cannot OHKO Meloetta at all.
Rotom-W is a good suggestion, although a bit risky. Of course, it can smack anything hard with Hydro Pump (even better in rain), but it's extremely risky to use any Electric move with a Choice item equipped. Thundurus can come in easily (maybe after you KOed something with Thunderbolt), set up NP and start to wreak havoc. You could come and revenge it later, however the shaky accuracy of Hydro Pump and the fact that it needs either SR or Rain to actually OHKO are letdown for sure. Still I prefer this to Starmie since it can easily switch into Metagross and take advantage of that. Maybe a SubSplit set would be interesting to consider, substituting on Metagross and hitting Thundurus with a LO Hydro Pump from behind a Substitute?
Jellicent is great to handle Metagross and completes our FWG core, but I feel it's a bit too much one-dimensional (it
only handles Metagross). Calcs provided by Temp V1 in his (hers?) analysis appear to be somewhat flawed, since I'm getting 58.91 - 69.3% damage for a LO Thunder from Meloetta-A on Specially Defensive Jellicent, that means you cannot switch in at all (Psychic deals 33% minimum, so Meloetta can 2HKO with Psychic + Thunder after SR). I'm not even running calcs for Thundurus. Of course you shut down Metagross, but I don't think this is enough to pick Jellicent right now.
I don't like
Tyranitar at all, especially the Scarf set suggested. Tyranitar makes us weaker to Fighting, Ground and Steel-type attacks, and due to its poor speed cannot revenge kill Meloetta-P at all (not sure if outspeeds even Thundurus, is the speed rounded up or down after Scarf boost?). It also cannot handle Metagross easily. If we choose this set, a Jolly nature is far better since it prevents Team 1 to prey on it with powerful, fast attackers like Terrakion, Infernape, Mienshao or whatever. Anyway, if we really want to run Sand (don't think it's a great idea at this point of the picking process), I think it's better to stick to Hippowdon, that can somewhat handle all those threats that Team 1 has already picked.
However, let me suggest another set. They opted for Earthquake over Hammer Arm on their Metagross, so I think it's mandatory to consider an Air Balloon Magnezone, that can set up on every move Metagross throws at him, eliminate it and deal quite a bit of damage to the rest of Team 2, also having the nice side effect of enabling us to take some powerful Dragon and overwhelm them after their Steel type is gone.
Magnezone @ Air Balloon
Trait: Magnet Pull
EVs: 36 HP / 252 SpA / 220 Spe
Nature: Timid
- Substitute
- Charge Beam
- Thunderbolt
- Hidden Power Ice
As already pointed out, Magnezone doen't care about Metagross at all (Meteor Mash fails to break Magnezone's Substitute, enabling it to rack up Special Attack boosts; even better if you manage to switch into EQ, being able to set up a lot of boosts with ease). After having set up and eliminated Metagross, it can smack both Team 1 remaining members with powerful attacks (BoltBeam coverage is nice here, since we don't really need HP Fire: Scizor is eliminated with Electric attacks, while Ferrothorn can't really do anything if it doesn't carry Bulldoze; and HP Fire would be quite weak in rain anyway) and hopefully open up holes that Team 2 can exploit. It also opens the road for an eventual Dragonite / Salamence / CM Lati@s / other Dragon to sweep, since Metagross is the main thing that keeps Team 1 from being swept by one of those.
EDIT: Looking back to the calcs, it's probably dangerous to set up on Meteor Mash. However, you can still reliably eliminate Metagross with Thunderbolt (2HKO 98.83% of the times with SR up); this is the worst case, however, and you still can set up without any problem on every other move.
EDIT2: I somewhat managed to forget about
Ferrothorn; let me comment about it now. Ferrothorn is great, especially in rain, however it doesn't seem to have great synergy with the rest of our core: it adds nasty weaknesses to Fire and Fighting, and cannot stop powerful Ground attacks, either. This means that something like non-choiced Terrakion, Lucario, Infernape (they still can go weatherless) or Mienshao can easily sweep us requiring only a free switch in; this is obviously undesirable, since all of those pokes fit perfectly in our opponents' strategy (all-out offensive or something similar). I think it's better to consider someone else to set up hazards, since taking Ferro to do so really exposes us too much to Fighting attacks (and to a lesser extent Fire).