Moves
Swords Dance allows Doublade to double its Attack, letting it attack powerfully. Shadow Sneak is Doublade's primary STAB move and somewhat makes up for its atrocious Speed, since it has boosted priority. Sacred Sword has perfect neutral coverage with Shadow Sneak and hits Normal-types immune to Ghost-type attacks, such as Chansey and Porygon2. It can also hit Dark-types that resist Shadow Sneak and threats that don't take much from Ghost-type moves, such as Tyranitar, Bisharp, and Ferrothorn. Shadow Claw is used because it is a strong STAB attack that has perfect neutral coverage with Sacred Sword. It also OHKOes Slowbro after two Swords Dances and helps against opposing Doublade. Iron Head can be used instead of Shadow Claw to hit Fairy-types such as Clefable and Togekiss harder, but they already take a lot of damage from Shadow Claw, and without Shadow Claw, Doublade loses to Slowbro and itself.
Set Details
Doublade's Attack is maximized and boosted with an Adamant nature in order to hit as hard as possible, OHKOing Victini with a +2 Shadow Sneak after Stealth Rock, for example. 36 Speed EVs let Doublade outpace Gastrodon and place it directly below Rhyperior, a target one wants to underspeed due to its use of a Weakness Policy. An alternative speed benchmark is 44 EVs, which lets Doublade outpace Rhyperior and potentially hit it with two +2 Shadow Claws, allowing Mega Scizor to clean up. The remaining EVs are placed into HP to boost Doublade's all-around bulk. Eviolite is Doublade's choice of item, as it makes Doublade's already great Defense stellar while patching up its horrible Special Defense. No Guard is Doublade's ability simply because it is the only option; it provides no added utility whatsoever, since all of Doublade's moves are perfectly accurate.
Usage Tips
Because Doublade can wall and set up on many physical attackers and Fighting-types such as Mega Heracross and Hawlucha, switch it into them. Also, switch Doublade into predicted Fighting-type moves and into Choice item users whose moves it resists or is immune to, including Choice Band Terrakion's Close Combat. However, due to its lack of recovery, preserve Doublade's health early-game, since it cannot sweep late-game if it is worn down earlier in the match. Doublade can also switch into certain Rapid Spin users, including Avalugg. Because the opponent will then most likely switch due to Doublade walling his or her Pokemon, either use an attack that hits the switch-in the hardest or set up a Swords Dance for free. If Doublade is a massive threat to the opponent's team and can exert offensive pressure from the beginning, such as against Psychic-type teams, it can do heavy damage early and allow a teammate to clean.
Two fantastic niches Doublade has are checking all Terrakion and non-Choice Band Victini, both of which are massive threats to Steel-type teams. It can force out the former by threatening super effective hits and tank the latter's V-create from full health to use Swords Dance and OHKO it with Shadow Sneak. It is best to keep entry hazards up on the opposing side, because they allow Doublade to more easily get crucial KOs, such as a guaranteed 2HKO against Victini and a guaranteed 2HKO against Latias and Latios after Stealth Rock. Conversely, keep hazards off one's own side of the field, since Doublade dislikes getting worn down due to a complete lack of recovery. Furthermore, keep Doublade away from Knock Off at all costs, since Doublade's Eviolite getting Knocked Off is disastrous for it. Additionally, zealously avoid Doublade getting burned, since a burn will negate any Swords Dances Doublade has set up and make it hit very weakly. It also dislikes the chip damage due to having no reliable recovery. Doublade can also be used as a pseudo-revenge killer, since it can KO a threat low on health with an unboosted Shadow Sneak.
Team Options
Because Doublade is easily KOed by many special attacks, specially defensive Heatran is a fantastic teammate, since it can tank them and receives free switches off of Doublade's weakness to Fire-type attacks while also providing chip damage with Toxic and Stealth Rock. Doublade's role in this partnership is to tank physical attacks that hit on Heatran's weaker defense while also being immune to Fighting-type attacks, to which Heatran is weak. Doublade partners well with entry hazard setters like Skarmory and Ferrothorn due to its immunity to Rapid Spin. Both can switch into Ground-type attacks that Doublade is weak to and net easier KOs for Doublade with the chip damage from entry hazards, a Rocky Helmet, Iron Barbs, and Leech Seed, respectively. Skarmory can also share the burden of checking Fighting-types with Doublade, while Ferrothorn allows it to outspeed Choice Scarf Hoopa-U and Choice Scarf Togekiss with Thunder Wave. Excadrill offensively synergizes excellently with Doublade, since it can outspeed and KO Choice Band Victini, Mega Charizard Y, and Bisharp, all of which are massive threats to Doublade. On the other hand, Magnezone can break bulky Water-types that Doublade struggles with, such as Suicune and Politoed. It can also gain momentum for Doublade's team with Volt Switch and trap Steel-types that beat Doublade, such as Knock Off Mega Scizor and Skarmory. Sweepers such as Bisharp and Mega Scizor work well with Doublade, since they share checks and can whittle them down until a sweep is possible. The former can deter Defog with Defiant, which Doublade dislikes due to hazards helping it sweep, while the latter can switch into Knock Off due to its irremovable item. Additionally, Mega Scizor can KO Choice Band Terrakion and TrickScarf Togekiss with Bullet Punch, two Pokemon Doublade dislikes.