Diancie

Mega Diancie's movepool may be somewhat limited, but when backed by high base Speed and attacking stats, it is able to propel Mega Diancie to the forefront of the Doubles metagame. Mega Diancie achieves solid mixed attacking coverage between two strong STAB attacks, with Earth Power filling in many of the few holes that are left. Using that coverage, Mega Diancie can take out many relevant threats such as Hydreigon, Heatran, Keldeo, and Mega Charizard Y. Perhaps Mega Diancie's greatest asset is found in its exclusive primary STAB move, Diamond Storm, which has everything a Doubles Pokemon could want: high Base Power, high accuracy, and a helpful secondary effect that gives some protection against physical attackers. Mega Diancie also has a superb ability in Magic Bounce, shielding it from moves that would otherwise severely hinder it such as Thunder Wave and Will-O-Wisp.

Unfortunately, a low HP stat further offset by uninvested defenses and weaknesses to decently common types in Water and Ground leaves Mega Diancie somewhat frail. More specifically, a weakness to the omnipresent Landorus-T's Earthquake makes it difficult for Mega Diancie to perform as well as it could otherwise. Having a low base Speed prior to Mega Evolving also holds it back, forcing it to rely on Protect to Mega Evolve safely. On the other hand, this low base Speed lets Diancie possess a little bit of flexibility in using its base forme to operate as a Trick Room setter with far more bulk than its Mega counterpart. Utilizing both Clear Body and a powerful Diamond Storm lets this set thrive in sweeping unprepared teams. However, Trick Room Diancie is hindered by the same critical typing weaknesses, as well as being countered by common Trick Room checks Amoonguss and Aegislash.