"Standard" formation: Regirock+Zapdos, Metagross & Latios in back.
Other options: Meta+Latios, Regirock & Zapdos in back. Regirock+Latios, Meta & Zap in back. Meta+Zap, Regirock & Latios in back.

Plan B formation: Regice+Moltres, anything in back.

These are only suggestions for starting points. During the tour, I got very creative with my leads, which was very beneficial against many opponents, particularly Nnico. Team Preview selection is not something that can be reduced to a science. Being unpredictable is valuable, as long as you're using good Pokemon (which I am here).

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Regirock is an amazing Pokemon, bulky, very hard to take down, has defensive synergy with Metagross, and is immune to Intimidate. The given EV spread aims to maximise its bulk against stuff like Starmie Hydro Pump (although Mystic Water still KOs). Good as a lead, good in the back, just a powerful Pokemon with lots of stats. Explosion is its biggest selling point, its other attacks feel more situational, relatively speaking. AncientPower is chosen over HP Rock for the negligible damage difference, and the chance to bail you out of dire situations with an omniboost. It has low PP but that never came into play (whereas the omniboost won me a game vs Nnico). Sometimes you just click AP into something just to fish for the boost. No shame in that!

Zapdos is the best Regirock partner, thanks to its positive matchup into Metagross (that threatens Regirock). A bulky spread was chosen due to the overall slower pace of the team, and due to Magnet originally being taken by Latios. You could probably run Timid Magnet if you wanted to (with Lum on Latios). Substitute was chosen to give Regirock/Regice/Metagross more opportunities to Boom next to it. The constant threat of Boom on basically every turn is a big selling point of this team.

Latios is the other good Regirock (and Metagross) partner. Calm Mind was chosen because it's simply really freaking good (OHKOing Starmie with Magnet Tbolt is less crucial on this team). I had a lot of dilemmas about what moves to run with Calm Mind. I think double STAB is a very solid choice however. Psychic allows you to still 2HKO Zapdos (barely), which I think is very valuable, as well as other random stuff like Arcanine. It's just big damage. For the other move you want something that hits both Latis and Metagross, and Dragon Claw is the only real option. You'll get many opportunities to click Calm Mind, especially when you're threatening Boom with your other Pokemon. Other sets are probably fine though, including 3-attack Magnet, or Substitute.

Metagross completes the "main core" of this team. Choice Band Metagross is an absolute beast, but you knew that already. I went for a more bulky spread due to the slower pace of the team, and due to the extra Attack not being particularly mandatory for most calcs (still KO Starmie, Latios, still 2HKO Zapdos with Shadow Ball). The extra bulk lets Metagross live two Zapdos Thunderbolts 19.9% of the time, which sounds pretty good to me. I went for a "compromise" spread with some extra Speed, because outspeeding other Metagross is obviously a big deal.

Moltres fits very well on this team in terms of synergy. It offers a more aggressive Metagross counter compared to Zapdos. Also, SpDef invested Moltres is genuinely a very good and reliable Pokemon. Will-o-Wisp is primarily for Snorlax. HP Grass for flexibility against Swampert.

Regice completes the team by adding another Boom option, being the only Special Wall on the team, and threatening KOs with Ice Beam on Latios/Zapdos (and breaking Subs with Icy Wind). It pairs particularly well with Moltres.

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The team felt very solid, and I never felt like I had a bad matchup. I got quite lucky against Shiritu & Nnico. Check out my interview on Nnico's stream for more thoughts on the run. I had an amazing set vs. Artcar, where I really had to explore the Regice+Moltres core to the fullest to succeed, props to them as well.

I strongly suggest using this team to anyone who feels inclined to do so. It is very fun, very balanced in terms of offense & defense, and will teach you a lot about type synergies. Also it's one of the best teams for Boom play, unsurprisingly.

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Orre Colosseum x Temple of Ra (22/9/24)

vs spibeder man
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250608
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250616

vs shiritu
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250658
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250668
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250677

vs Artcar
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250690?p2
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250695?p2
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250700?p2

vs Nnico
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250712?p2
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250720?p2
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250723?p2

GFs
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250736
https://replay.pokemonshowdown.com/dawn-gen3orrecolosseum-250737