The oldest Pokemon returns, in His fossil form, to the treacherous environment known the BW Uber metagame, by holding a Stone Plate. While He has not been given anything new other than the ability to use full EVs, Rock Arceus can now effectively counter quite a few new Pokemon. With excellent all-round stats, He is one of the few Pokemon who can boast being able to counter both Ho-Oh and Reshiram. In sandstorm, His Special Defense is so massive that even unfathomably powerful attacks such as Draco Meteor from Choice Specs Dialga simply bounce straight off. Rock Arceus is possibly one of the most versatile and unpredictable Arceus formes, being able to utilize Calm Mind and Swords Dance with equal efficiency, while also being able to serve as a fantastic support Pokemon.
This is not to say that Rock Arceus is without His downsides. While His defenses are phenomenal, especially in a sandstorm, His Rock typing gives Him weaknesses to five very common attacking types. A susceptibility to all three forms of entry hazards and somewhat of an over-reliance on weather in a tier littered with Toxic Spikes and weather changers do not help His cause, either. Use Rock Arceus to His advantages and He will be a great asset, but you must be aware of His weaknesses.
Rock Arceus's huge bulk and great STAB allow it to run an effective mono-attacking set. This set is useful for a number of reasons. First, with sandstorm support and its pure Rock typing, Arceus is a fantastic counter to many dangerous Pokemon. With its Rock-type Judgment, it can quickly put Ho-Oh and Reshiram in their place; with Will-O-Wisp, it can easily cripple Normal Arceus, making it an excellent check to the Extreme Killer while maintaining a STAB with decent coverage. Under sandstorm, it can also switch into some of the most powerful special attacks in the Uber tier. For example, Draco Meteor from Modest Choice Specs Dialga only does 53.60% - 63.51%, allowing Rock Arceus to heal off the damage and stall Dialga out. Second, access to Calm Mind lets Rock Arceus switch from a defensive Pokemon into a deadly sweeper in the blink of an eye, and any team that lacks an appropriate counter for it will quickly be crushed. This allows Arceus to easily control the tempo of the match, switching between offense and defense at will. While this set is at its best on sandstorm teams, its utility does not end there. On a sun team, it works as an excellent check to opposing Fire-types, who become even more dangerous in the sun.
Calm Mind is obviously the crux of the set, boosting Arceus's excellent Special Attack to levels where it can sweep, while skyrocketing its already bloated Special Defense to untouchable levels. Judgment is obviously Arceus's STAB, while Recover allows it to switch in and tank hits again and again. The last slot comes down to the user's preference. Will-O-Wisp complements Calm Mind and Judgment almost perfectly, enabling Arceus to cripple physical attackers such as Groudon and Garchomp. Refresh, on the other hand, allows Arceus to laugh off status, especially from the likes of Blissey and Chansey.Team Options & Additional Comments >>>
While the previous set focuses on using Rock Arceus's defensive capabilities to pull off a sweep, this set takes full advantage of its excellent Special Attack, Speed, bulk, and coverage to pull off a sweep as quickly as possible. After a single Calm Mind, Arceus reaches a maximum of 558 Special Attack, with which it can deal huge amounts of damage to weakened teams. Judgment is Arceus's STAB attack, which hits most Pokemon that do not resist it extremely hard. Fire Blast allows Arceus to roast Steel Arceus that might attempt to Calm Mind alongside it, as well as other Steel-types, such as Ferrothorn and Jirachi. Grass Knot, on the other hand, lets Rock Arceus destroy any Groudon and Kyogre that think they can change the weather and stop Arceus with their super effective STAB attacks. Recover is preferred in the last slot, as it enables Arceus to still check dangerous threats such as Reshiram and Ho-Oh, but an additional coverage move can be used for maximum coverage.Team Options & Additional Comments >>>
Rock Arceus is one of the select few Arceus formes that can viably run a Swords Dance set, and also the only Swords Dance Arceus that can defeat Skarmory without depending on weather. While Swords Dance Arceus may seem more appealing than its Calm Mind counterpart due to its ability to boost more quickly, Swords Dance Arceus does have a few disadvantages. Firstly, it can no longer switch into Ho-Oh as easily, as Sacred Fire has a 47.5% chance of crippling it, factoring in accuracy. Secondly, it is very easily walled, especially by Groudon, who poses a huge threat to sandstorm teams in general. That being said, Swords Dance Rock Arceus is still an extremely potent sweeper. To illustrate its power, after a single Swords Dance, Jolly Arceus can OHKO specially defensive Skarmory after Stealth Rock damage most of the time. Stone Edge is Rock Arceus's powerful—albeit inaccurate—STAB attack; STAB Stone Edge is what differentiates Rock Arceus from Ground Arceus, who can run a similar set. Earthquake gives Arceus fantastic coverage alongside Stone Edge. Recover allows Arceus to recover lost health and check threats such as Reshiram more easily.Team Options & Additional Comments >>>
While Arceus has an abundant special movepool to work with, none of its other options add more coverage than what is recommended. Flamethrower can be used if you find Fire Blast's accuracy off-putting. Focus Blast hits Steel-types and Dialga super effectively in place of Fire Blast, but its inaccuracy makes it a poor option. Thunder hits Kyogre extremely hard while having a high paralysis chance, but as Grass Knot does the same amount of damage to Kyogre, Thunder is generally not preferred.
Rock Arceus can run a mono-attacking Swords Dance set with Swords Dance, Recover, Refresh, and Rock Slide, but Calm Mind is generally better; regardless, such a set is much easier to wall. Arceus can run a rather useful dual screens set, as well as a very bulky Cosmic Power stall set. It can also drop Calm Mind on the mono-attacker set to run a full support set with Roar, Perish Song, or Stealth Rock in its place, should you desire it.
Checks and Counters
As alluded to in the individual set descriptions, Fighting Arceus is Rock Arceus's number one enemy. As it resists Rock Arceus's STAB and is neutral to Rock Arceus's commonly used coverage moves, it can easily set up Calm Mind alongside Rock Arceus and take it down with a super effective Fighting-type Judgment. Steel and Ground Arceus can work in a similar fashion, but need to watch out for Fire Blast and Grass Knot, respectively. Grass and Water Arceus both have a super effective Judgment to use on Rock Arceus as well, but need to watch out for Fire Blast and Grass Knot, respectively, while boosted neutral Rock-type Judgments will also hurt.
Any special variant of Rock Arceus that lacks Substitute or Refresh is walled by Chansey and Blissey, who can both shrug off any attack Arceus can throw at them and cripple Arceus with Toxic. If Arceus lacks Grass Knot or Will-O-Wisp, Groudon can switch in without fear and KO it with Earthquake. Garchomp works in a similar vein, only fearing the rare Ice Beam, whereas Excadrill can switch into anything not named Earthquake, Will-O-Wisp, or Fire Blast, and KO with Earthquake. Kyogre causes problems for special variants of Rock Arceus that lack Grass Knot, as its enormous Special Defense allows it to tank anything Rock Arceus throws at it, while Arceus is forced to switch to avoid taking STAB Water-type attacks to the face. Choice Scarf Kyogre can outspeed and OHKO Rock Arceus with Water Spout, even after a Calm Mind. Choice Scarf Terrakion and Heracross can revenge kill weakened Rock Arceus, the latter also enjoys being burned by Will-O-Wisp. Groudon and Ground Arceus will have a field day against Swords Dance Rock Arceus, while Giratina and Ferrothorn can use Will-O-Wisp or Leech Seed to stall out Rock Arceus. Be aware that should Arceus carry Overheat, Ferrothorn should stay well away unless it has rain support.