Deoxys-D appears to be a potent wall at first glance. It has a wide support movepool, having access to Knock Off to annoy potential switch-ins, a semi-exclusive entry hazard in Spikes, and reliable recovery. Furthermore, its Speed, while not excellent, is high enough for it to outspeed most other walls. Deoxys-D's Psychic typing also seemingly lets it act as a check to threatening Psychic-types, such as Deoxys-A. Unfortunately, in practice, Deoxys-D is a terrible Pokemon in Ubers. Its excellent defenses are undermined by its horrible HP, which significantly detracts from its bulk and leaves it vulnerable to very powerful attacks, such as most Z-Moves. Deoxys-D is also very passive, rendering it susceptible to Taunt. However, Deoxys-D's greatest flaw lies in its typing, which is simply not conducive to its role as a wall. A mono-Psychic typing offers Deoxys-D little in the way of useful resistances, fails to protect it from entry hazards and Toxic, and burdens it with awful weaknesses to Ghost- and Dark-type moves, which are extremely common in Ubers. This means that it confers virtually no defensive benefit to teams, making it a dreadful wall. Due to this multitude of crippling flaws, Deoxys-D offers nothing over other defensive users of Spikes, such as Skarmory, Ferrothorn, and Klefki, all of which can check a wider variety of Pokemon and disrupt opposing teams more effectively. Do not use Deoxys-D.
move 1: Spikes
move 2: Recover
move 3: Knock Off
move 4: Toxic
evs: 252 HP / 252 Def / 4 SpD
Spikes allows Deoxys-D to make use of free turns, punishing the opposing team by wearing down grounded Pokemon that switch in. Recover increases Deoxys-D's staying power and allows Deoxys-D to Toxic stall the few Pokemon that cannot break through it. Knock Off prevents Deoxys-D from being total Taunt bait, OHKOes Deoxys-A, and punishes switch-ins by removing their items; for example, Ferrothorn and Celesteela, which would otherwise totally wall Deoxys-D due to their Toxic immunity, are crippled by the loss of their Leftovers. Toxic lets Deoxys-D cripple switch-ins, such as Giratina-O, support Arceus formes, and the plethora of offensive Pokemon that can take advantage of it, such as Yveltal. Taunt is also an option, as it allows Deoxys-D to prevent slower walls that it cannot touch, such as Ferrothorn, from setting up on it.
Maximum investment in HP and Defense alongside a Bold nature maximizes Deoxys-D's physical bulk. Leftovers gives Deoxys-D access to passive recovery.
Switch Deoxys-D into Pokemon that cannot break through it, such as specially defensive Primal Groudon, Magearna, and Zygarde-C. Use its free turns well, as its passivity and vulnerability to a myriad of common threats mean that it should not be kept in play for longer than a few turns at most. Spikes should be set whenever it is safe to do so, but bear in mind that Deoxys-D's bad matchup against most Pokemon in Ubers renders opportunities to set up Spikes infrequent. If it is obvious that something that can easily take advantage of Deoxys-D, such as a setup sweeper, defensive Spiker, or Defog user, is going to switch in, use the appropriate move to cripple them before switching Deoxys-D out. Should Deoxys-D actually succeed in its intended roles of stacking Spikes and walling Psychic-types, feel free to sacrifice it to allow another teammate safe entry into play.
Stealth Rock users such as Primal Groudon and Dialga can form a hazard stacking core with Deoxys-D. As Deoxys-D is extremely vulnerable to Dark-types, Pokemon that can deal with them, such as Xerneas, Arceus-Fairy, and Magearna, make for useful teammates. Xerneas in particular appreciates Deoxys-D's ability to slowly wear down its checks with Spikes. Arceus-Dark, Yveltal, and Darkrai can beat Ghost-types, which otherwise easily take advantage of Deoxys-D. Most wallbreakers, such as Swords Dance Primal Groudon, Calm Mind Primal Kyogre, Zekrom, and Palkia, and sweepers, such as Mega Salamence and Mega Lucario, are greatly assisted by Spikes.
Deoxys-D can act as a Stealth Rock user, using whatever free turns it can get to set up multiple entry hazards. However, Stealth Rock exacerbates Deoxys-D's already severe four-moveslot syndrome, making it a poor option. Magic Coat allows Deoxys-D to frustrate Pokemon that attempt to set up hazards or inflict status conditions on it. However, Magic Coat is very reliant on good prediction to succeed, which can result in dire consequences should you mispredict and give the opponent a free turn. Skill Swap allows Deoxys-D to bypass Mega Sableye. With good prediction, it can also bother switch-ins; for example, using Skill Swap on a predicted Mega Gengar switch-in allows Deoxys-D to switch out and potentially gain momentum for its team. However, it is usually not worth sacrificing a moveslot for the sole purpose of annoying a single Pokemon when Deoxys-D already has problems doing its job as is. Ice Beam lets Deoxys-D check Mega Salamence and Zygarde-C, as well as chip away at Pokemon that lack reliable recovery, such as Primal Groudon. However, it has no other use and comes at the expense of a utility move, making Deoxys-D even worse at supporting its team. If Deoxys-D wishes to improve its matchup against Mega Gengar, it can run Shed Shell over Leftovers so that it is not affected by Shadow Tag. However, this deprives Deoxys-D of important passive recovery, forcing it to rely more on Recover to keep healthy than it would like to.
Checks and Counters
**Mega Sableye**: Mega Sableye can switch into Deoxys-D if it attempts to use Spikes or Toxic and simply reflect both moves with Magic Bounce, making Deoxys-D useless. However, Mega Sableye's usefulness as a check diminishes if Deoxys-D is running Skill Swap.
**Ghost-types**: Arceus-Ghost can either set up Swords Dance on Deoxys-D or simply OHKO it with an unboosted Never-Ending Nightmare. Mega Gengar easily traps and removes Deoxys-D; this vulnerability is magnified if Mega Gengar is carrying Taunt, as Deoxys-D becomes almost defenseless against it in this scenario and is forced to retaliate with weak Knock Offs. Aegislash 2HKOes Deoxys-D with Shadow Ball and is immune to Toxic. Lunala can either 2HKO Deoxys-D with Moongeist Beam or use it as setup fodder. Giratina-O can remove Deoxys-D's entry hazards with Defog and threaten it with a super effective Hex or Shadow Force.
**Dark-types**: Calm Mind Arceus-Dark hard counters Deoxys-D, as it can circumvent status with Refresh and laughs at its other moves. Yveltal, Alolan Muk, Choice Band Tyranitar, and Darkrai can overwhelm Deoxys-D with their super effective STAB attacks.
**Setup Sweepers**: If Deoxys-D lacks Taunt, it becomes setup fodder for a plethora of setup sweepers. Swords Dance Primal Groudon, Calm Mind Primal Kyogre, Mega Lucario, Geomancy Xerneas, and most Swords Dance Arceus formes, among others, can all take advantage of Deoxys-D's passivity and set up in its face.
**Taunt Users**: Faster Pokemon that carry Taunt, such as Mega Mewtwo Y and Deoxys-S, prevent Deoxys-D from doing anything useful.
**Entry Hazard Setters**: If it is not carrying Taunt, Deoxys-D becomes setup bait for other Spikes users, such as Ferrothorn, Skarmory, and Klefki; these Pokemon also happen to be immune to Toxic by virtue of their Steel typing, leaving Deoxys-D helpless against them.