Moves
Draco Meteor is the move Dragalge will be using the vast majority of the time. Thanks to the move's massive 130 Base Power, Adaptability boost, and Choice Specs boost, it is able to do a massive amount of damage to anything but Fairy-types, Chansey, and Blissey. It's able to OHKO frailer Steel-types such as Bisharp as well as 252 / 0 Mew after Stealth Rock damage. Fairy-types, the absolute best switch-ins to Draco Meteor, are, barring Klefki, annihilated by Dragalge's secondary STAB move, Sludge Wave. Sludge Wave also gives Dragalge a much more reliable STAB move with which it can hit both Grass-types and neutral targets hard without having to suffer from Draco Meteor's Special Attack drop. Focus Blast allows Dragalge to hit common Steel-type switch-ins, such as Ferrothorn, Bisharp, and Heatran as well as Tyranitar. However, if you don't mind being worse off against Heatran, and would much rather have better accuracy and the ability to demolish Mega Scizor, Hidden Power Fire can be used in lieu of Focus Blast. Scald lets Dragalge check Heatran, mostly if Dragalge isn't running Focus Blast. Scald doubles as a move with almost no drawbacks, and it can be used early-game to fish for a burn on some of Dragalge's most common switch-ins, such as Klefki, Jirachi, and Mega Metagross.
Set Details
In order to outspeed Hippowdon, which would otherwise cripple Dragalge with Earthquake, it's recommended for Dragalge to run 28 Speed EVs. Because Dragalge is a specially based wallbreaker, maximum Special Attack EVs are used. Likewise, Choice Specs is the recommended item for the set, as it is capable of boosting all of Dragalge's moves to their highest possible power. The remaining EVs are thrown into HP because Dragalge enjoys having mixed bulk. 140 Speed EVs, at expense of HP, can be used if you desire Dragalge to outspeed Calm Mind Clefable and Tyranitar so that Dragalge can hit them with Sludge Wave or Focus Blast, respectively. If Dragalge is using Hidden Power Fire, only 136 Speed EVs would be needed, as outspeeding Tyranitar wouldn't be a priority.
Usage Tips
Dragalge has excellent special bulk, respectable physical bulk, and a unique defensive typing; exploit all of these characteristics! Dragalge can easily pivot into many threatening Pokemon in OU, including Keldeo, Mega Charizard Y, Rotom-W, Mega Manectric, Raikou, Clefable, and Thundurus; tank a hit; and proceed to fire off a ridiculously powerful move on whatever decides to switch in. The majority of the time, the only button you'll be clicking is Draco Meteor, but if the opponent has bulky Steel- or Fairy-types, more prediction will be necessary. Don't be too shy about using Sludge Wave; despite its lower power compared to Draco Meteor, it still can accomplish absurd feats such as OHKOing Keldeo after factoring in Stealth Rock damage.
Team Options
Despite Dragalge's access to Focus Blast, Hidden Power Fire, and Scald, it is still going to have immense troubles with Steel-types. Magnezone is an excellent partner for its trapping ability. Dragalge's low Speed and four common weaknesses also leave it prone to being revenge killed. For instance, Psychic-types, such as Mega Gardevoir and Latios, can easily KO Dragalge after Draco Meteor's Special Attack drop. A Pursuit trapper, such as Tyranitar, is thus a useful teammate. Mega Metagross also makes for a great teammate because of its ability to check both Mega Gardevoir and Latios. Finally, Dragalge is prone to being revenge killed by Excadrill; to remedy this weakness, Rotom-W and Celebi can serve as great teammates.
Trick Room staples such as Bronzong, Cresselia, Porygon2, and Crawdaunt can make for good teammates as well, as Dragalge's terrible Speed stat, while normally a huge flaw, can allow it to sweep under Trick Room. Defensive cores are also plausible, as Dragalge, even without any Special Defense investment, has solid bulk and a great typing. Skarmory resists all of Dragalge's weaknesses except Ice, while Dragalge resists both of Skarmory's weaknesses. Needless to say, these two work really well together, with Dragalge able to deal out serious damage and act as a generic check to special attackers and Skarmory acting as a mixed wall capable of setting and removing entry hazards. Unaware Clefable also can make for a good teammate, as it can heal off any damage Dragalge might take with Wish. It also can serve as a lure for Poison-type moves, which gives Dragalge opportunities to switch in, and heal off any burns Dragalge might have taken with Heal Bell. Other Fairy-types, including Azumarill, Gardevoir, and Sylveon, can similarly lure in Poison-types for Dragalge to switch into. Mega Gyarados also can make for a good teammate; Dragalge can KO Keldeo, Dragon-types, Azumarill, Chesnaught, and Ferrothorn for Mega Gyarados, while Mega Gyarados can set up on Ground-types and Heatran, both of which give Dragalge trouble. Mega Diancie also makes for a good teammate, as it and Dragalge have a lot of checks in common and therefore can break down the other Pokemon's answers. Dragalge baits in and wears down Mega Scizor and Ferrothorn, which opens up the opportunity to sweep for Diancie. In turn, Diancie can take on Jirachi and Heatran better than Dragalge can thanks to its access to Earth Power.