Mega Diancie so far seems pretty interesting (well, to me at least). The following post will probs just be theorymonning, but w/e.
So, if I were to distribute Mega Diancie's 100 BST increase to its original form's largest stats equally, it will look something like this: 50/120/180/120/180/50
This is a lot cooler than you think. It lets Diancie check Zekrom, Ho-Oh, Yveltal, Ray, MegaBlaze, and Darkrai. That's pretty darn good to say the least (tho I might be overstating it), even with the fact that it might not get any reliable recovery. Here are some calcs with the above BST (WALL OF CALCS INCOMING):
252+ Atk Teravolt Zekrom Bolt Strike vs. 252 HP / 252+ Def Diancie: 121-144 (39.8 - 47.3%) -- guaranteed 3HKO
252+ Atk Teravolt Zekrom Bolt Strike vs. 252 HP / 0 Def Diancie: 154-183 (50.6 - 60.1%) -- guaranteed 2HKO
252+ Atk Ho-Oh Earthquake vs. 252 HP / 0 Def Diancie: 144-170 (47.3 - 55.9%) -- 79.3% chance to 2HKO
252+ Atk Ho-Oh Earthquake vs. 252 HP / 252+ Def Diancie: 112-134 (36.8 - 44%) -- guaranteed 3HKO
252+ Atk Life Orb Ho-Oh Earthquake vs. 252 HP / 0 Def Diancie: 187-221 (61.5 - 72.6%) -- guaranteed 2HKO
252+ Atk Life Orb Ho-Oh Earthquake vs. 252 HP / 252+ Def Diancie: 146-174 (48 - 57.2%) -- 90.6% chance to 2HKO
252+ Atk Mega Blaziken Flare Blitz vs. 252 HP / 0 Def Diancie: 75-89 (24.6 - 29.2%) -- 99.9% chance to 4HKO
+6 252+ Atk Mega Blaziken Flare Blitz vs. 252 HP / 252+ Def Diancie: 235-277 (77.3 - 91.1%) -- guaranteed 2HKO
252+ Atk Mega Blaziken Low Kick (20 BP) vs. 252 HP / 252+ Def Diancie: 21-25 (6.9 - 8.2%) -- possibly the worst move ever
252 SpA Life Orb Darkrai Focus Blast vs. 252 HP / 252+ SpD Diancie: 82-97 (26.9 - 31.9%) -- guaranteed 4HKO
252 SpA Life Orb Darkrai Focus Blast vs. 252 HP / 0 SpD Diancie: 104-123 (34.2 - 40.4%) -- guaranteed 3HKO
(Ik Focus Blast is rly bad on Darkrai this gen but its the strongest move it can use against Diancie)
So, most of the above threats need boosts or LO (except Zekrom) to break past Diancie, and the above physical threats can just be hit by Diamond Storm and have Diancie's Defense go up even higher. With this knowledge, we can make 2 sets with Diancie's known movepool and these stats:
Physically Defensive (or Specially Defensive)
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name: fucking guess
move 1: Diamond Storm
move 2: Stealth Rock
move 3: Moonblast
move 4: Hidden Power Fire / Trick Room
ability: ???
item: ???
EVs: 252 HP / 252 Def / 4 SpD or 252 HP / 4 Def / 252 SpD
nature: Relaxed (or Sassy)
I am actually quite interested in what Mega Diancie will bring to the table with its typing and movepool (Trick Room support sounds evil), especially since its ability hasn't been confirmed yet but Trollfreak will strike again and give it Clear Body again.
inb4 Steel Wing Ygod.