This is exciting, I've been waiting to make this post since Typing.
For our Calm Mind/Recover set, I propose the two move combination of Dark Pulse and Moonblast. This post is mostly going to be made in comparison to/contrast with the Dark Pulse/Sludge Bomb set that was mentioned by pretty much everyone else thusfar.
First and foremost, something that I think is fantastic about this combination, in contrast to Dark Pulse/Sludge Bomb, is that it can reliably hit almost every unbanned CAP and Pokemon in existence neutrally at worst with 3 non-viable exceptions in Galarian-Weezing, Mawile, and Klefki. Its combinations of Fairy/Poison, Fairy/Steel, and Fairy/Fire that are the only things that resist this combination, giving us plenty of power for what may very well be a pair of non-STAB moves thanks to our ability, giving us nice universal breadth and coverage.
Second, on the topic of STAB, when we switch in we will start with a Dark typing to give Dark Pulse its STAB. Ordinarily, that also applies to Sludge Bomb. However, when we change type, that sometimes changes to something inconvenient. Currently, it is safe or advantageous for us to switch in against a number of common Fairies such as Jumbao, Tapus, and Clefable, who we pressure by existing and the threat of Sludge Bomb. Not having Sludge Bomb however is not a major loss, in my eyes. If we switch in against a Fairy move, we change into Fairy, a unique interaction that we can take advantage of offensively with exactly this set. Fairy is neutral against all Fairies in the game except for those non-viable 3 mentioned earlier, and more importantly, neutral against everyone we would be switching in against. This gives us STAB pressure as a switch in, which we can still take advantage of offensively against the Fairy who hit us, and more importantly, gives us an against whoever switches in after the Fairy retreats. A switch out from Jumbao to Landorus or Garchomp for example will remain neutral or even become Special Effective rather than not very effective from the hypothetical Sludge Bomb that scared out the Fairy, and also potentially retains STAB. This is an interaction that I think is extremely interesting, taking our disadvantageous ability, and smartly using it to our advantage not just defensively as was extensively discussed thusfar, but also using it to our advantage offensively.
Third comes the shift in who we pressure. Sacrificing the Sludge Bomb does hurt with Rillaboom and Tangrowth, but our Fairy Matchups are all still strong. For example, if we switch in against a Tapu Lele, it will either use a non-effective Psychic move that forces it to switch out, a Moonblast that changes us to the advantageous Fairy type, or a Focus Blast. It doesn't matter what our 2 attacking moves are, we can set up for free against Moonblast/Focus Blast on a choice specs set with our stats. The Tapu has no choice but to switch out. However with this switch (and really, for all of the Fairies we pressure other than Koko), we can potentially retain our powerful Fairy typing. As for which matchups become advantageous, we very crucially threaten a lot of Pokemon such as Colossoil, Garchomp, and most noteably Tomohawk, giving us a nicer list of pressures based on movepool.
Finally, its worth talking about the drawback. Aside from not threatening to immediately kill Fairies, and the aforementioned hurt to Rillaboom/Tangrowth, this set does still remain weak to Blissey, Toxapex, Gastrodon, and defensive Heatran. However, these are still things that threaten the standard Sludge Bomb/Dark Pulse sets, meaning that these 4 remain as counters. Likewise, Moonblast struggles to deal with Steels and Poisons offensively, but that is not a significant change from Sludge Bomb having the same problems. In other words, Moonblast has a lot of weaknesses in common with Sludge Bomb. This means that an opponent is not playing an infinite guessing game like Bulletproof/Levitate Equilibra, but has some semblance of consistency they can fall back on, keeping it as a healthy matchup. The biggest thing we are losing is the 30% chance to poison, the initial STAB, and the Rillaboom matchup. However, considering the discourse on Scald/Dark Pulse, I don't think that the lack of the initial STAB/Rillaboom matchup effectiveness is all doom and gloom.
TLDR In Conclusion:
- Moonblast/Dark Pulse is a pretty much unresisted combo
- We still threaten Fairies. If we switch in against them and become Fairy, we are more threatening even after they run away
- We can cover a few more major threats such as Tomohawk
- A lot of the counters that can check Sludge Bomb also check Moonblast, such as Heatran and Toxapex
Therefor: Moonblast / Dark Pulse is the way to go.