Deoxys-D is an often overlooked Pokemon, and for good reason. While it has great defensive stats, its HP is lacking, and it simply can't stand up to the powerhouses that rampage through the Uber tier. It also receives competition from its sibling formes, most of which can play the support role better. Despite its tragic shortcomings, Deoxys-D can still help a team out with its fairly vast support movepool. However, it will need some assistance itself; do not expect to be able to just throw it onto a team and have it work for you. It may not be the first Pokemon you consider for your team, nor should it be, but it can certainly perform its roles well when given a chance.
While it may not be the best choice for setting up Spikes, Deoxys-D can certainly pull its weight. Though it has great Special Defense and Defense stats, they are unfortunately let down by a rather poor HP stat. The first slot goes to Spikes, allowing Deoxys-D to support the team by limiting the amount of switches the opponent can perform. Deoxys-D faces tough competition from Forretress, Skarmory, and Deoxys-S for a team slot, since all of them are also very competent at setting up Spikes; however, Deoxys-D has some advantages over the other Spikers. Deoxys-D boasts far higher Special Defense than Skarmory, but doesn't have the handy Steel typing that Skarmory does. Forretress is often used over Deoxys-D because it can also learn Toxic Spikes and Rapid Spin, but Deoxys-D has Recover, so it isn't completely outclassed by Forretress either. Finally, Deoxys-S is mainly used as a suicide lead, whereas Deoxys-D's superior bulk allows it to function well throughout the game.
To keep Deoxys-D in tip-top condition, Recover is the preferred move in the second slot. Toxic works great in conjunction with Recover as it allows Deoxys-D to effectively stall out many threats with its decent bulk. The last slot is a bit of a toss-up. Ice Beam is useful to give Deoxys-D some form of offense, and has the ability to hit the multitude of Dragon-type Pokemon in Ubers for a hefty amount of damage. On the other hand, Taunt can be used to prevent Pokemon such as Forretress from setting up on Deoxys-D.Team Options & Additional Comments >>>
While it may seem silly on paper, this set can be quite effective and aggravating to an opponent when used correctly. This set functions quite similarly to Mewtwo's Toxic Stalling set, although Mewtwo performs a little bit better due to its superior Speed, which enables it to forgo Agility for either Reflect or Light Screen. Mewtwo also has access to Will-O-Wisp, which it often uses over Toxic and alongside one of the aforementioned screens to shut out attackers of all types. Make no mistake, however, that while this set may be outclassed, Deoxys-D can still hold its own.
Agility is the most important move on this set as, with the given EVs, it allows Deoxys-D to outspeed max Speed Deoxys-S, enabling Deoxys-D to Taunt Deoxys-S before it receives a Taunt in return. Agility also gives Deoxys-D enough Speed to outspeed Choice Scarf Garchomp, the fastest commonly used Choice Scarf user in Ubers. Deoxys-D has extremely poor attacking stats, so Toxic is used to allow Deoxys-D to stall out everything but Steel- and Poison-type Pokemon, the latter of which is almost never seen in Ubers. Taunt protects Deoxys-D from status and prevents opposing walls from recovering health or healing status. It also saves Deoxys-D from being Taunted, as Deoxys-D outspeeds every non-Choice Scarfed Pokemon─and therefore every Taunt user─after an Agility. Recover allows Deoxys-D to constantly heal while the opponents' Pokemon slowly die to poison damage.Team Options & Additional Comments >>>
Deoxys-D has a few other options not mentioned in the above sets, though most are gimmicky. A lead set is possible, but it is inferior to Deoxys-S in nearly every way. Calm Mind can be used to attempt to create a bulky setup sweeper, but its Special Attack is so low that it barely even scratches the majority of Ubers with its feeble assaults. A CounterCoat set is usable, but is unreliable and Deoxys-D has such low HP that it won't be bouncing much damage back anyway. Cosmic Power is an interesting choice to raise both of Deoxys-D's great defenses, but Deoxys-D is still vulnerable to Taunt and every Steel-type in Ubers. Using Light Clay with Reflect and Light Screen is plausible, but this set is severely outclassed by other dual screens users. Finally, Psycho Shift and Rest are both interesting options to rid Deoxys-D of status, but it usually has better things to do.
Checks and Counters
Heracross can switch into anything Deoxys-D throws at it, especially Toxic thanks to Guts, and proceed to Megahorn Deoxys-D into oblivion. If Deoxys-D doesn't have an Agility boost under its belt, fast Taunt users like Mewtwo and Darkrai beat it and set up with ease. Tyranitar doesn't really care what Deoxys-D does and can do massive damage with STAB Dark-type attacks, notably Pursuit if Deoxys-D tries to switch out.
Deoxys-D cannot stand up to the likes of Choice Specs Dialga or Choice Specs Kyogre. Most Steel-types also wall Deoxys-D, as it has poor attacking stats and relies on Toxic for damage. Scizor can switch in and hit Deoxys-D with a powerful U-turn. Jirachi can paralyze Deoxys-D even when Taunted, thanks to Body Slam, and proceed to flinch it to death with Iron Head. Heatran has a 4x resistance to Ice Beam, the only attack that Deoxys-D ever carries and can torch Deoxys-D with sun-boosted Fire-type attacks. If Deoxys-D lacks Taunt, it can easily be Toxic stalled by Blissey with Aromatherapy. Even without Aromatherapy, Blissey can just heal itself of poison with Natural Cure.