Moves
STAB Psycho Boost deals massive damage to most Pokemon that don't resist it. However, the move harshly lowers Deoxys-A's Special Attack, making it prone to being forced out or being used as setup fodder afterwards.
Ice Beam hits common Psychic-type switch-ins like Yveltal, Ultra Necrozma, and Lugia super effectively and OHKOes Zygarde-C and Mega Salamence. Its decently high Base Power, perfect accuracy, and good neutral coverage make it an attractive option to pick off weakened foes without incurring unnecessary stat drops from Psycho Boost.
Superpower hits Dark- and Steel-types like Ferrothorn, Arceus-Dark, and Tyranitar and lets Deoxys-A muscle past Chansey and Blissey. It's preferred over Low Kick because it deals more damage to light targets like Magearna, Klefki, and Chansey and Blissey, although it has the downside of becoming weaker with each consecutive use.
Pursuit lets Deoxys-A trap Mega Gengar, which it naturally forces out; Pursuit trapping utility is appreciated by teammates like Arceus-Fairy that are vulnerable to Mega Gengar. It's also useful to ensure damage on other threats such as Ultra Necrozma and Mega Mewtwo Y.
Dark Pulse hits Psychic- and Ghost-types like Necrozma-DM, Lunala, and Mega Gengar super effectively. It also hits Ultra Necrozma hard whether or not it decides to Ultra Burst so Deoxys-A isn't forced to guess between Ice Beam and Superpower.
Spikes is a good option to take advantage of the many switches Deoxys-A forces. A conservative opponent who constantly switches their defensive answers into Deoxys-A as it uses Spikes will find their team under substantial pressure from Spikes later in the match. It also forces Yveltal into mind games over whether or not it should use Sucker Punch.
Knock Off can be used instead of Dark Pulse for its added utility of removing items. This is useful for punishing checks that hold Leftovers like Necrozma-DM, Magearna, and Lugia, as well as for Choice Scarf users like Yveltal and Lunala that may try to pivot into Deoxys-A. However, it's worse against Pokemon that hold irremovable items such as Necrozma-DM with Solganium Z or Ultranecrozium Z and Magearna with Normalium Z.
Extreme Speed allows Deoxys-A to pick off faster attackers like Choice Scarf Xerneas and Yveltal once they have been severely weakened.
Set Details
Maximum Speed investment with a Naive nature lets Deoxys-A outspeed Mega Mewtwo Y and +1 base forme Zygarde.
A Rash nature can be used instead to give Deoxys-A more firepower while still letting it outspeed key threats like Mega Gengar, Ultra Necrozma, and Arceus formes. Notably, Deoxys-A gets a much better chance to OHKO offensive Yveltal with Ice Beam and, after Stealth Rock damage, to OHKO bulky Yveltal with Ice Beam and maximum HP Arceus formes with Psycho Boost.
Life Orb boosts the damage output of Deoxys-A's attacks, making it much harder to wall. Due to its frailty, Deoxys-A doesn't mind the recoil that Life Orb inflicts.
Usage Tips
Deoxys-A is best used as a wallbreaker that punches holes into the opponent's team in order to give teammates an easier time cleaning up.
Prediction is a key factor when utilizing this set. Using Psycho Boost as the opponent switches to a Pokemon resistant or immune to it like Necrozma-DM or Choice Scarf Yveltal will cost Deoxys-A a ton of momentum and often force it out afterwards.
Be wary of creating setup opportunities for sweepers like Necrozma-DM after using Psycho Boost. If Deoxys-A's teammates cannot handle these sweepers, Deoxys-A should avoid using Psycho Boost until these threats have been removed or sufficiently weakened to the point where they can no longer set up safely.
Scout for potential Choice Scarf users like Xerneas and Yveltal, since they outspeed Deoxys-A and can easily OHKO it with their attacks.
Despite having a higher base Speed, Deoxys-A is generally forced out by Yveltal even if the latter has been weakened. Choice Scarf variants outspeed Deoxys-A, while non-Choice Scarf variants often carry Sucker Punch. Thus, it's best to catch Yveltal on the switch with Ice Beam or, if possible, completely remove it from play beforehand instead of confronting it directly.
Deoxys-A can't really switch into attacks due to its nonexistent bulk. It's best brought in via free or double switches, pivoting moves, or the predicted use of a status move like Stealth Rock.
Pursuit should be used against Pokemon that Deoxys-A naturally forces out, such as Mega Gengar and Ultra Necrozma. Note that Pokemon like Gothitelle and Lunala with Shadow Shield intact are likely to stay in against Deoxys-A.
Setting Spikes is an aggressive play you can make when you think the opponent will try to pivot around Deoxys-A or sacrifice a Pokemon to it. A switch may be likely if the opponent has a healthy check to Deoxys-A or needs to preserve the Pokemon that they currently have on the field.
Team Options
Deoxys-A's frailty means that it will have few opportunities to switch in and wallbreak. Thus, it fits primarily on fast-paced offensive teams.
Teammates that can pressure Deoxys-A's checks make for good offensive partners. Primal Groudon, Marshadow, and Calm Mind Arceus-Ground pressure Steel-types for Deoxys-A, while Arceus-Fairy and Xerneas deal with Dark-types for it.
Setup sweepers like Rock Polish Primal Groudon, Trick Room Necrozma-DM, and Dragon Dance Mega Salamence have an easier time cleaning up once Deoxys-A has punched holes in the opposing team.
Geomancy Xerneas and Naganadel are notable partners, since they share checks with Deoxys-A in Necrozma-DM and Magearna. Deoxys-A or its partner can get damage on these checks to increase the likelihood that the other one will sweep.
Pokemon that can deal with Deoxys-A's revenge killers are appreciated. Arceus-Fairy and Choice Scarf Xerneas can deal with Marshadow and Yveltal, two of the most common ones. Marshadow offensively checks common priority users such as Extreme Killer Arceus and Mega Lucario. Chople Berry Extreme Killer Arceus lures Marshadow and Mega Lucario for Deoxys-A and can pivot into Choice Scarf Lunala.
Tapu Lele provides Psychic Terrain support for Deoxys-A, which augments its wallbreaking and sweeping capabilities. Psychic Terrain negates a key weakness to priority moves and substantially increases the power of Psycho Boost to the point where it can overwhelm even bulky Psychic-resistant Pokemon, such as Magearna and Mega Scizor.
Bulky offensive teams can provide VoltTurn support to bring Deoxys-A in safely. Magearna can pivot into Choice Scarf Xerneas and Yveltal, two of Deoxys-A's most common revenge killers, and use Volt Switch to get Deoxys-A in safely. Choice Scarf Yveltal can pivot into Ghost-type attacks from Marshadow and Lunala, while Mega Scizor handily checks Xerneas, and they can use U-turn to bring Deoxys-A in.
Entry hazard support is great for wearing down Deoxys-A's checks. Stealth Rock setters like Primal Groudon and Arceus-Fairy keep Pokemon like Ho-Oh and Yveltal in line. Skarmory, Ferrothorn, and Klefki are viable Spikes setters, and while some of them don't fit on offensive teams, they can still pair nicely with Deoxys-A. Skarmory can easily handle Necrozma-DM and Mega Scizor, Ferrothorn can switch into Magearna and support variants of Necrozma-DM, and Klefki can pivot into Choice Scarf Xerneas and Yveltal for Deoxys-A.