Diancie

Upon Mega Evolving, Diancie gains an incredibly useful new ability, Magic Bounce. Mega Diancie is also graced with powerful base 160 offensive stats coupled with a fast base 110 Speed. These stats when combined with its Rock / Fairy typing allow it to check common threats such as Darkrai, Yveltal, Ho-Oh, Latias, and Lugia. Regular Diancie is no slouch either; although its offenses are low, its bulk can be quite useful, and it doesn't take up a Mega slot. Despite having some key resistances, Diancie is hampered by a 4x weakness to Steel and a weakness to common Ground-type moves. While Diancie does have access to useful support moves such as Heal Bell, Stealth Rock, and Trick Room, its lack of instant recovery is quite disappointing. Diancie's movepool on the offensive side is somewhat similar, as it can make use of two excellent STAB moves and Earth Power but does not have many other tricks. Both Diancie and Mega Diancie are stuck with a low base 50 HP, and Mega Evolving Diancie proves quite difficult, as it keeps its low Speed for that turn while losing a lot of its bulk.