Gen 9 NU Grassy Terrain Sweeper

Dastardly (Drifblim) @ Grassy Seed
Ability: Unburden
Tera Type: Electric / Poison
EVs: 80 Def / 16 SpA / 168 SpD / 244 Spe
Modest Nature
IVs: 0 Atk
- Shadow Ball
- Air Slash
- Calm Mind
- Strength Sap
A Calm Mind set Drifblim can use on Grassy Terrain teams in Gen 9 NU. Yes, I'm aware another user posted a moveset with the same 4 moves on this set, but this one uses a different version, ability, nature, and EV spread. How the moveset works is simple. At some point when Grassy Terrain is up, you need to get Drifblim in so it can consume its Grassy Seed to give Drifblim a defense boost and activate Unburden to enable Drifblim to outspeed the entire unboosted meta and some of the boosted meta. Calm Mind lets Drifblim raise its Special Attack and Special Defense to become a potent wincon that can be hard to knock out. Strength Sap allows Drifblim to recover HP and cripple physical wallbreakers by lowering their attack stat, giving Drifblim more opportunities to get off multiple Calm Mind boosts. Shadow Ball and Air Slash are the chosen attacking moves for this set, with Shadow Ball providing Drifblim with a consistent STAB move to use against Pokemon who aren't immune to or resist Ghost moves, and Air Slash allowing you to hit Ghost resists and immunities such as Scrafty and Cinccino. Also, Air Slash allows you to be like Oricorio-Pa'u and flinch its way past Pokemon it would struggle against. Also, no Pokemon in the meta resists Ghost and Flying moves outside of the very rare Naclstack. (Morpeko isn't real in the NU meta)
Tera Electric allows Drifblim to become immune to paralysis that could slow it down and cripple it. Tera Electric is also nice to make Flamigo think twice about clicking Brave Bird. Tera Poison is an option to have a Toxic immunity while still being able to resist Fighting moves. These Tera Types can allow Drifblim to actually get a little HP recovery from Grassy Terrain. Also, both of these Tera Types appreciate Grassy Terrain up to halve Earthquake damage. Since this set is used on Grassy Terrain teams, Thwackey is a required teammate to enable Grassy Terrain for Drifblim.
The given EV spread allows Drifblim to outspeed Choice Scarf Munkidori after consuming Grassy Seed while avoiding the 2HKO from (non Tera Psychic) Psychic Munkidori if Drifblim didn't get off a Calm Mind boost. Keep in mind this is the case if you did NOT Tera into a Poison type. 16 Special Attack EVs with a Modest Nature gives Drifblim a jump point for its Special Attack stat. The rest of the EVs are used in Defense since Drifblim is one of those Pokemon with a really high HP stat but low defenses, so there wasn't a point in investing in HP. Here are some other EV spreads you could use for Drifblim (All of them use Modest Nature):
EVs: 72 Def / 16 SpA / 168 SpD / 252 Spe (basically same idea but with max speed Modest)
EVs: 96 SpA / 168 SpD / 244 Spe (just enough to outspeed Scarf Munkidori, uses extra EVs in Special Attack while still getting a jump point in its Special Attack stat)
EVs: 88 SpA / 168 SpD / 252 Spe (Max speed Modest and dumping the rest of the EVs in Special Attack)
EVs: 4 Def / 252 SpA / 252 Spe (If you want an offensive EV spread, keep in mind you miss out on avoiding the 2HKO from Psychic from Munkidori without the 168 Special Defense EVs)