Arceus-Steel can check an interesting range of Pokemon, such as Mega Salamence lacking Earthquake, some Xerneas variants, Arceus-Fairy, Mega Diancie, Magearna, Tyranitar, and Alolan Muk, thanks to its useful resistances to Fairy, Flying, Rock, and Poison. Arceus-Steel is also one of two Arceus formes that are immune to poison, allowing it to pressure and set up on Pokemon that rely on status to do significant damage, such as Blissey. Unfortunately, Arceus-Steel's defensive utility is heavily impacted by its debilitating weaknesses to extremely common types in Fire, Fighting, and Ground. Arceus-Steel is also very vulnerable to omnipresent and dangerous threats such as Arceus-Ground, Primal Groudon, Primal Kyogre, Ho-Oh, and Marshadow. This means that Arceus-Steel generally adds more defensive flaws to a team than it solves. Arceus-Steel is a rather poor choice as a team's Steel-type, as it cannot be relied on as a team's primary Xerneas check; Xerneas that carry Focus Blast can blow right through Arceus-Steel. Arceus-Ground, Arceus, and Arceus-Poison are generally better choices as Swords Dance Arceus formes due to their greater power, superior utility, ability to better check specific Pokemon, or any combination of these traits.
name: Swords Dance
move 1: Swords Dance
move 2: Iron Head
move 3: Earthquake
move 4: Stone Edge / Extreme Speed
item: Steelium Z
evs: 252 Atk / 4 SpD / 252 Spe
Swords Dance improves Arceus-Steel's otherwise poor offensive presence. Iron Head is Arceus-Steel's most viable physical STAB move. As a Z-Move, Iron Head becomes Corkscrew Crash, which deals over 89% to all 252 HP support Arceus formes neutral to the move after a boost and OHKOes Giratina-O and Mega Salamence after Stealth Rock, with the latter benchmark being particularly important if Stone Edge is not opted for. Earthquake allows Arceus-Steel to hit Primal Groudon and Toxapex, which otherwise wall it. Stone Edge ensures Arceus-Steel is not Ho-Oh fodder and allows Arceus-Steel to hit Mega Salamence super effectively. Extreme Speed can be run to pick off weakened Pokemon if Ho-Oh is already properly accounted for, but it offers no extra coverage. Recover is an option to increase Arceus-Steel's durability and somewhat improve its matchup against defensive teams, but it offers neither the coverage of Stone Edge nor the utility of Extreme Speed, leaving Arceus-Steel more easily walled.
Maximum investment in Attack and Speed with a Jolly nature ensures Arceus-Steel hits as hard as possible and can Speed tie at worst with Mega Salamence and other offensive Arceus formes. Steelium Z is necessary to give Arceus-Steel access to one use of Corkscrew Crash.
Arceus-Steel can be switched into Pokemon such as Stealth Rock + Toxic Arceus-Fairy, defensive Mega Salamence, Magearna, Clefable, defensive Tyranitar, Z-Geomancy Xerneas, and Kyurem-W locked into Ice Beam. Defensive Pokemon such as Blissey and Chansey are also fair game due to their reliance on Toxic to do any damage; Arceus-Steel's immunity to the move gives it slightly more leeway than most Swords Dance Arceus formes. Do not try to set up while Arceus-Steel's numerous checks are still alive; either pivot Arceus-Steel out of the predicted switch-in or apply pressure with an offensive move. Corkscrew Crash is somewhat predictable due to the lacking power of Iron Head prohibiting Arceus-Steel from accomplishing much, so do not be reckless with it. Only when Arceus-Steel's checks are sufficiently worn down or removed can a sweep can be attempted.
Stealth Rock users, such as Primal Groudon and Excadrill, are important to ease the matchup against Ho-Oh and Lugia, especially if Arceus-Steel has forgone Stone Edge, and to ensure Corkscrew Crash hits necessary damage benchmarks. Checks to Primal Groudon, such as Mega Salamence and Giratina-O, and to Ho-Oh, such as Mega Diancie and Zygarde-C, are also imperative for Arceus-Steel to function. A secondary Xerneas check is necessary due to Arceus-Steel's inability to check Xerneas running Focus Blast; Primal Groudon and Ho-Oh can fill this role. Fire-types such as Primal Groudon and Ho-Oh can check levitating Steel-types, which totally wall Arceus-Steel. Primal Groudon can also check Primal Kyogre for Arceus-Steel. Choice Scarf Yveltal provides an immunity to Ground-type moves and can check Marshadow for Arceus-Steel; Arceus-Steel can check certain Fairy-types, such as Magearna, and Tyranitar in return. Other Marshadow checks worth considering include Landorus-T, which also provides Arceus-Steel's team with a Ground immunity, and Zygarde-C. Xerneas is a good teammate, as it appreciates Arceus-Steel's ability to act as a hard stop to Magearna. Mega Gengar can trap and eliminate Leftovers Skarmory and Bronzong for Arceus-Steel; Arceus-Steel can defeat Alolan Muk and Tyranitar in return. Primal Kyogre can check most variants of Arceus-Ground.
A Calm Mind set can bother some defensive teams, which typically rely on Toxic to check Calm Mind Arceus formes, but Ho-Oh and Haze Toxapex's high prominence on these teams makes this a bad idea. Defog sets are not worth using due to their significant vulnerability to Primal Groudon and Stealth Rock Arceus-Ground making them inefficient hazard removers. Iron Plate can be run over Steelium Z if your team already has a Z-Move user, but it makes Arceus-Steel very weak and makes breaking through teams quite difficult.
Checks and Counters
**Levitating Steel-types**: Celesteela, Bronzong, and Skarmory are the hardest counters available to Arceus-Steel, as they resist Iron Head and Extreme Speed, can easily take Stone Edge, and are immune to Earthquake. This lets them use Arceus-Steel as setup fodder.
**Marshadow**: Marshadow is faster than Arceus-Steel and can even switch into an unboosted Iron Head. Spectral Thief does excellent damage to Arceus-Steel if it has boosted with Swords Dance, making setting up very difficult if Marshadow is on the opposing team. Alternatively, Life Orb Marshadow has the option of simply OHKOing Arceus-Steel with Close Combat.
**Ground-types**: Primal Groudon can switch into Arceus-Steel quite easily, only fearing a boosted Earthquake, and OHKO Arceus-Steel with Precipice Blades. Swords Dance Arceus-Ground Speed ties with Arceus-Steel and threatens to OHKO it with Tectonic Rage. A transformed Zygarde-C can take a boosted Corkscrew Crash when its health is above 57%, but its matchup against Arceus-Steel is awkward, as a boosted Corkscrew Crash threatens to OHKO regular Zygarde after some prior damage. Landorus-T can take a boosted Corkscrew Crash from full health due to Intimidate and do heavy damage to Arceus-Steel with Earthquake.
**Fire-types**: Ho-Oh easily defeats Arceus-Steel with Sacred Fire if Arceus-Steel is not running Stone Edge, but it is an unsafe switch-in otherwise. Mega Blaziken cannot switch into Arceus-Steel, but Protect variants can revenge kill it with Flare Blitz or Low Kick.
**Super Effective Coverage**: Arceus-Steel's common weaknesses leave it vulnerable to super effective coverage moves from the Pokemon it is supposed to check, such as Earthquake Mega Salamence, Fire Blast Mega Mewtwo Y, Fire Blast Arceus-Dragon, Focus Blast Xerneas, and Superpower Deoxys-A. However, none of these Pokemon find it easy to switch into Arceus-Steel, as they fear a boosted Corkscrew Crash or Extreme Speed in the case of Deoxys-A.
**Primal Kyogre**: All variants of Primal Kyogre can easily switch into Arceus-Steel due to their resistance to Steel and do heavy damage with Primordial Sea-boosted Water-type moves. Offensive Primal Kyogre even has a very small chance to OHKO Arceus-Steel from full health with Origin Pulse.
**Physically Defensive Pokemon**: Giratina and Buzzwole can take a boosted Corkscrew Crash from full health and Roost off the damage or phaze Arceus-Steel with Dragon Tail, respectively. However, Giratina's lack of reliable recovery makes it a slightly worse answer to Arceus-Steel.