Celebi
Typing: Grass/Psychic -----> Grass/Psychic
Abilities: Natural Cure -----> Gardener (Summons Grassy Terrain upon switch-in)
BST: 100/100/100/100/100/100 -----> 100/130/130/130/130/80
New Moves: Grassy Terrain
Anyone who's watched the Celebi movies knows about its forest powers. This Mega focuses on that ability, its role as a protector of nature, the voice of the forests. First off is its improved defenses, sporting a nice 100/130/130 bulk. This comes at the cost of some Speed, in exchange for Celebi being better able to take hits. It also gets a small boost to its offenses, raising each to a decent 130. Now, for a legendary, especially a Mega, this may all seem a bit underwhelming. That is, however, until one takes a look at its ability. Gardener summons Grassy Terrain upon switch-in for 5 turns, helping Celebi in a few ways. Firstly, it provides some nice passive healing while it is in effect, helpful for a Pokemon with Celebi's bulk. Secondly, it boosts the power of Grass-type moves by 1.5x. This means both its physical and special Grass-type attacks will be coming off of a whopping
195 Attack/Special Attack stat while Grassy Terrain is in effect--stronger than Mega Mewtwo Y. With this, Celebi will really be able to live up to its role as protector of the forest, ripping through anything that doesn't resist Grass-type attacks--that's just what keeps it in check, though. Yes, with Grassy Terrain, Celebi does indeed have amazingly powerful Grass-type attacks, but
only Grass-type attacks get the boost, and as we all know, Grass isn't exactly the best offensive typing. There are plenty of things in OU that can resist these moves with ease. Additionally, while 100/130/130 bulk is nice, Grass/Psychic typing isn't nearly as good defensively. Sporting weaknesses to common types like Fire and Dark, Celebi will face some trouble against more common threats it would like. However, when played correctly and with some team support, Celebi can be a great force to be reckoned with.