Arceus-Grass has a clear niche in Ubers as a hard counter to Arceus-Ground and Arceus-Rock and as a solid check to Arceus-Water and defensive variants of Primal Kyogre. Arceus-Grass's unique mono-Grass typing gives it a key resistance to Ground and a neutrality to Rock, which allows it to also deal with threatening sweepers such as Primal Groudon that lack a Fire-type move. Despite its common weaknesses to Flying-, Ice-, and Fire-type moves, Arceus-Grass can be difficult for offensive teams to switch into due to its potent coverage that can easily overcome would-be checks, such as Rayquaza, Mega Salamence, and Mega Lucario. Several balance cores, such as Primal Kyogre + Celesteela and Primal Kyogre + Arceus-Ground, also struggle to deal with Arceus-Grass, which can make it surprisingly dangerous in some matchups. Unlike most offensively inclined Arceus formes, Arceus-Grass can afford to invest in bulk due to Grass Knot having a Base Power of 144 against most Ubers Pokemon.
Unfortunately, Arceus-Grass's many weaknesses make it difficult to bring into play, as many Pokemon carry moves that can hit it super effectively. This diminishes its effectiveness in practice. Arceus-Grass also struggles with four-moveslot syndrome, as it is forced to run Grass Knot, Ice Beam to lure and KO Mega Salamence, and Recover to ensure it remains useful throughout a match. This means it cannot run both Stone Edge and Fire Blast and is forced to settle for the latter move due to it hitting a wider breadth of Pokemon, rendering it extremely weak to Ho-Oh. While Arceus-Grass has a decent matchup against offensive teams, it has a terrible matchup against stall teams, where checks such as Toxapex, Ho-Oh, and Lugia are ubiquitous and render Arceus-Grass dead weight. This is complicated by how common defensive teams are in the Ubers metagame. Arceus-Grass also is very vulnerable to status, especially poison and paralysis, and has a very poor matchup against Mega Gengar. Arceus-Grass's positive qualities allow it to function very well in certain matchups, but it requires considerable team support to overcome its offensive and defensive shortcomings. This can make it difficult to justify on most teams.
name: Offensive Utility
move 1: Grass Knot
move 2: Ice Beam
move 3: Fire Blast
move 4: Recover
item: Meadow Plate
evs: 252 HP / 4 SpA / 252 Spe
Grass Knot 2HKOes Arceus-Ground, Arceus-Water, Primal Kyogre, all offensive Primal Groudon, and Arceus-Rock. Ice Beam prevents Arceus-Grass from being bait for several dangerous threats in Ubers, OHKOing offensive Mega Salamence and Rayquaza and 2HKOing Zygarde-C and offensive Yveltal after Stealth Rock. Fire Blast lets Arceus-Grass do solid damage to most Steel-types. It always OHKOes Ferrothorn, OHKOes Mega Lucario after a small amount of prior damage, deals over 44% damage to Celesteela, and 2HKOes other niche Steel-types such as offensive Solgaleo and Mega Metagross. Recover allows Arceus-Grass to remain a threat throughout a match and prevents it from being easily worn down by chip damage from entry hazards and weak attacks. Stone Edge can be run over Fire Blast to KO a lured Ho-Oh after Stealth Rock, but it is often not worth eschewing Fire Blast's ability to hit most Steel-types. Opting for Stone Edge also makes Arceus-Grass Spikes bait for Ferrothorn and Skarmory, which is not ideal.
252 HP EVs ensure that Arceus-Grass is never 2HKOed by defensive Primal Kyogre's Ice Beam at full health and allow it to better take weak attacks from the Pokemon it is supposed to check without having to rely on Recover. Another minor benefit is that Sludge Wave from Mega Gengar will never OHKO Arceus-Grass, even if it has switched into Stealth Rock once. 252 Speed EVs alongside a Timid nature let Arceus-Grass Speed tie at worst with Mega Salamence and allow it to outspeed all support Arceus formes.
Pivot Arceus-Grass into Pokemon that it forces out, such as Arceus-Ground, Zygarde-C, and Arceus-Water. Arceus-Grass is also an effective switch-in to Primal Groudon lacking a Fire-type move, but you should ensure you know Primal Groudon's moveset before taking it on. Once Arceus-Grass is in play, the best course of action is often to use the move that hits the predicted switch-in super effectively; however, if Arceus-Grass is at low health and the Pokemon it checks are still alive, use Recover when possible. Against offensive teams, Arceus-Grass must be played carefully, as a misprediction can be very costly and give the opponent free turns. Arceus-Grass struggles with very bulky teams due to its lack of power; play it aggressively against these teams to allow a teammate a chance to put in work. Once Arceus-Grass has removed the specific Pokemon it checks or lures in, it can be sacrificed to maintain your team's momentum.
Stealth Rock setters are imperative to ensure that Ho-Oh is punished for switching into Arceus-Grass. Dialga makes for a particularly good setter, as it can further punish Ho-Oh with Toxic. In return, Arceus-Grass can anti-lead Mega Lucario predicting what may appear to be an obvious Dialga lead. Rock Polish Primal Groudon benefits from Arceus-Grass's ability to destroy support Arceus formes that give it problems, as well as harass Steel-types; in return, Primal Groudon provides an additional check to Primal Kyogre and can deal with Ho-Oh and Poison-types such as Toxapex. Mega Lucario benefits greatly from Arceus-Grass's ability to remove Arceus-Water and Arceus-Ground. Stone Edge variants can lure in Ho-Oh for Arceus-Grass in return. Facade Mega Salamence can deal with Ho-Oh and also appreciates Arceus-Grass's ability to soften up several Steel-types. If a defensive check to Ho-Oh is desired, Zygarde-C is also an effective choice. Giratina-O can remove entry hazards that pressure Arceus-Grass into using Recover and strengthen the team's ability to deal with Arceus-Ground and Primal Groudon; Giratina-O can also remove Mega Gengar with Shadow Sneak. Z-Geomancy Xerneas appreciates Arceus-Grass's ability to soften up Steel-types that would otherwise easily deal with it. Aromatherapy variants are also good options, as they can remove status from Arceus-Grass. Tyranitar and Alolan Muk can Pursuit trap Mega Gengar; Tyranitar can also deal with Ho-Oh, while Alolan Muk can absorb Toxic Spikes and beat Clefable. Both of these Pokemon appreciate Arceus-Grass's ability to beat Arceus-Ground in return. Taunt Mega Gengar can stallbreak for Arceus-Grass, defeat Clefable, and remove Toxic Spikes from play.
Magic Coat can be extremely annoying to support Arceus formes trying to inflict status on Arceus-Grass, but it's impossible to fit on the moveset and is reliant on flawless prediction. Using four attacks on Arceus-Grass may seem appealing to maximize coverage, but this is generally a bad idea as Arceus-Grass will really miss the durability that Recover brings. A more offensive spread with maximized Special Attack 2HKOes support Arceus formes neutral to Grass Knot if Stealth Rock is up, but it doesn't achieve any other notable benchmarks and sacrifices any defensive utility Arceus-Grass has. Icy Wind slows Mega Gengar and will still overcome Rayquaza and Mega Salamence foolhardy enough to switch in. However, Ice Beam hits a wider variety of targets, specifically Yveltal, and removes any chance of these Pokemon being able to revenge kill Arceus-Grass. A defensive set is usable, but it is too passive to function in SM Ubers. Arceus-Grass also has a bad typing for a defensive set due to its common weaknesses. Thunder Wave can cripple Mega Gengar but is hard to fit and unreliable. Judgment is slightly more consistent than Grass Knot, notably 2HKOing Marshadow, but fails to hit several damage benchmarks; for example, it will never 2HKO offensive Primal Groudon at full health. Do not use Bloom Doom, as it is a terrible option that hits Pokemon for only marginally higher damage than a maximum-strength Grass Knot.
Checks and Counters
**Special Walls**: Arceus-Grass cannot touch Blissey, Chansey, or Clefable. All three of them are specially bulky enough to easily shrug off Grass Knot and can use Arceus-Grass as setup fodder.
**Poison-types**: Mega Gengar can trap and remove Arceus-Grass with Sludge Wave, but Arceus-Grass's HP EVs are optimized such that Sludge Wave will never OHKO it, even if it has taken Stealth Rock damage. This means that Mega Gengar risks being 2HKOed by Fire Blast if it switches into Arceus-Grass while Stealth Rock is up prior to Mega Evolving. Toxapex and Tentacruel completely wall Arceus-Grass and can use it as setup fodder for Toxic Spikes. Arceus-Poison hard counters Arceus-Grass due to its natural type advantage and can use it as setup fodder for Swords Dance.
**Ho-Oh**: Ho-Oh completely walls Arceus-Grass if it lacks Stone Edge. Offensive Ho-Oh OHKOes Arceus-Grass with Brave Bird, while defensive Ho-Oh can cripple Arceus-Grass with Toxic.
**Lugia**: Even if Multiscale is broken, Lugia can still easily take Ice Beam and proceed to Toxic stall Arceus-Grass.
**Mega Blaziken**: Mega Blaziken walls Arceus-Grass and can use it as fodder for Swords Dance.
**Yveltal**: At full health, Yveltal can switch into Ice Beam and respond with a super effective Oblivion Wing, 2HKOing Arceus-Grass and recovering more health than Arceus-Grass can remove with successive Ice Beams. Yveltal cannot safely switch into Arceus-Grass if Stealth Rock is up, however.
**Dragon-types**: Dialga's Dragon typing means that Arceus-Grass can only hit it for neutral damage with Fire Blast. This means that Dialga can use Arceus-Grass as setup fodder for Stealth Rock, inflict Toxic upon it, or 2HKO it with Fire Blast. Support Arceus-Dragon will win one-on-one against Arceus-Grass, as it can stall out Ice Beam with Recover. Both Giratina formes can deal with Ice Beam well enough to use Arceus-Grass as Defog bait, but Giratina-O can be worn down quickly if it switches in repeatedly. Reshiram takes little damage from Ice Beam and possesses a quadruple resistance to Grass Knot and Fire Blast, allowing it to easily switch into Arceus-Grass and OHKO it with Blue Flare.
**Ice-types**: Arceus-Ice cannot safely switch into Arceus-Grass if Stealth Rock is up, as Arceus-Grass Speed ties with it and will almost always 2HKO it with Fire Blast. However, at full health, Arceus-Ice can safely switch in and defeat Arceus-Grass with a combination of super effective Judgment and Recover. Kyurem-W can easily switch into Arceus-Grass that lack Stone Edge and OHKO it with Ice Beam after a small amount of prior damage.
**Revenge Killers**: Under Psychic Terrain, Deoxys-A can OHKO Arceus-Grass with Psycho Boost. However, it will lose if Psychic Terrain is not up and Arceus-Grass is at full health. Mega Mewtwo Y takes very little damage from Grass Knot due to its low weight, outspeeds Arceus-Grass, and can 2HKO it with Fire Blast. However, Mega Mewtwo Y will take a lot of damage if it switches into Grass Knot prior to Mega Evolving.
**Primal Groudon**: Arceus-Grass cannot safely switch into Primal Groudon that carry a Fire-type move, as even Lava Plume from the specially defensive set 2HKOes it. Mixed Rock Polish and Rock Polish + three attacks variants of Primal Groudon can revenge kill Arceus-Grass, as they can take Grass Knot, set up Rock Polish, and OHKO Arceus-Grass with Fire Blast and Fire Punch, respectively. However, offensive sets reliant on EdgeQuake coverage will lose, and support sets that forgo Lava Plume can only respond with Toxic.