Dragalge

Based on stats alone, there are much more powerful specially based available Dragon-types such as Latios and Latias; why would you use a Pokemon with a mere base 97 Special Attack? Furthermore, Dragalge is the slowest fully evolved Dragon-type in the game. Alongside its defensive typing, and in the context of the OU metagame, this means it has to worry about being revenge killed by many top-tier threats, including Mega Charizard X, Excadrill, Landorus-T, Mega Alakazam, Mega Medicham, and Latios.

However, by virtue of that same defensive typing, Dragalge is able to find a place on many teams as a tank, capable of handling many common threats, including Mega Charizard Y, Keldeo, Gengar, Clefable, Manaphy, Mega Manectric, Rotom-W, Thundurus, and Mega Venusaur. Regardless of the set, Dragalge's ability Adaptability (which bolsters the power of its STAB moves by a total factor of 2), is a great boon. Dragalge is also able to differentiate itself from other Dragon-types thanks to its access to STAB Sludge Wave, which powers through many common Fairy-types, including Clefable, as well as its secondary Poison typing, which renders it neutral to Fairy-type moves to which Latios or Latias would fall. Dragalge also provides additional utility with Toxic Spikes, which allows it to cut into the longevity of foes such as Substitute Calm Mind Keldeo. However, do not assume Dragalge needs Toxic Spikes to function; it can also use a devastating Choice Specs set capable of achieving feats such as OHKOing Mew, Keldeo, and Zapdos.