Usage stats are also out, with whatever we can gleam from those.
Attendance has continued to drop, down to 10173 players (plus another 1285 in juniors)--predictable, since the prize of 50 BP is far less impressive than previous prizes (hell, it's not even enough to buy a single mega stone at the battle tree!) and general waning enthusiasm in the lull up to US/UM.
Once again defying description, the masters usage stats imply a total of just 11980 Pokemon across all the teams, which would require almost everyone to go into team preview with five blank slots on their team, and that clearly wasn't the case. More likely, it's leaving certain teams out of consideration for the usage stats entirely, though on what standards, no one can be sure (less than X battles? final rating less than Y?)
The number may in fact be a bit higher than 11980, but that has to do with the system I use to try and discern exactly how many copies of everything were in use on the set of teams that were being considered. That has to do with the details page: if you click one of the Pokemon icons there, you'll see a list of up to 10 most-frequently-used moves, items, natures, and abilities (though in this last case there will of course never be more than 3). What's notable about those lists is that precision is displayed to the tenth of a percent, but already this tells us a key point:
however many times this Pokemon appears in the stats, it must be a number that's capable of being the denominator of a fraction that rounds to that percentage, and likewise that must continue to be true for up to 32 more distinct percentages. For example, if there were something that had listed percentages of 5.0%, 10.0%, 15.0%, and so on with nothing smaller than 5.0, the obvious conclusion is that there were 20 data points being sampled there. It might not necessarily be correct--the number could actually be 40, backed by the enormous coincidence of every move/item/nature appearing an even number of times--but especially given the individuality shown in movesets, and in random natures among players who don't care to optimize for those, 20 is the overwhelmingly most likely candidate to be the true total when faced with a data set like that.
This analysis is completely hopeless at discerning the true answer when that answer is 1000 or higher, and especially with the reduced eligibility field (only 43 Pokemon) compared to last month's No Holds Barred, the high end of the usage rankings must at the very least be dangerously close to that 1000 cutoff, if not surpassing it. But descending just a bit down the rankings, we can start to find a clear order that makes sense, and is also consistent with the ordinal rankings they show for the top 30. In each case here, I've taken the
lowest population count that can possibly be consistent with all the reported percentages, and assuming that is in fact the true number, divided out how many of each Pokemon were in fact holding their mega stone:
Charizard
892 (533 Mega Y, 330 Mega X, 26 other items, 3 itemless)
Salamence
781 (731 Mega, 43 other items, 7 itemless)
Garchomp
714 (101 Mega, 608 other items, 5 itemless)
Metagross
692 (602 Mega, 87 other items, 3 itemless)
Blaziken
633 (354 Mega, 274 other items, 5 itemless)
Gyarados
630 (440 Mega, 187 other items, 3 itemless)
Kangaskhan
628 (587 Mega, 40 other items, 1 itemless)
Mawile
488 (469 Mega, 19 other items)
Gengar
466 (308 Mega, 154 other items, 4 itemless)
Venusaur
443 (419 Mega, 23 other items, 1 itemless)
Blastoise
433 (389 Mega, 43 other items, 1 itemless)
Gardevoir
421 (358 Mega, 61 other items, 2 itemless)
Slowbro
342 (291 Mega, 49 other items, 2 itemless)
Lucario
340 (274 Mega, 62 other items, 4 itemless)
Tyranitar
326 (213 Mega, 110 other items, 3 itemless)
Lopunny
324 (322 Mega, 2 other items)
Altaria
281 (271 Mega, 10 other items)
Sableye
269 (149 Mega, 120 other items)
Aggron
248 (178 Mega, 70 other items)
Scizor
240 (172 Mega, 68 other items)
Alakazam
231 (176 Mega, 54 other items, 1 itemless)
Manectric
202 (192 Mega, 10 other items)
Swampert
190 (118 Mega, 69 other items, 3 itemless)
Latios
170 (55 Mega, 113 other items, 2 itemless)
Aerodactyl
155 (117 Mega, 34 other items, 4 itemless)
Heracross
148 (123 Mega, 24 other items, 1 itemless)
Gallade
140 (129 Mega, 11 other items)
Sceptile
113 (84 Mega, 29 other items)
Latias
104 (71 Mega, 33 other items)
Ampharos
102 (86 Mega, 15 other items, 1 itemless)
Sharpedo
97 (67 Mega, 30 other items)
Medicham
83 (68 Mega, 15 other items)
Pidgeot
76 (72 Mega, 3 other items, 1 itemless)
Glalie
73 (21 Mega, 51 other items, 1 itemless)
Beedrill
70 (all of which were Mega)
Steelix
67 (50 Mega, 17 other items)
Absol
67 (45 Mega, 20 other items, 2 itemless)
Pinsir
66 (54 Mega, 10 other items, 2 itemless)
Abomasnow
58 (28 Mega, 30 other items)
Houndoom
50 (38 Mega, 12 other items)
Banette
49 (48 Mega, 1 other item)
Camerupt
47 (43 Mega, 4 other items)
Audino
31 (30 Mega, 1 itemless)
In all, at least 9279 out of the 11980 Pokemon I can account for (77.5%) were holding mega stones--a slightly higher number than I would have expected prior to the event starting, but a lower number than I would have guessed in retrospect.
My own team for the occasion was only half megas, and perhaps shaped by those decisions, I kept making safe plays to cover for potential gimmicks like Sash, when in fact only one of the opponents I ever faced all tournament was using a non-mega (the ever-exciting Mawile vs. Sableye Metal Burst mirror, out of 20 battles total with a 14-6 record).
Predictably, Garchomp had the lowest usage of its mega stone as a percentage of all its appearances; Latios, Glalie, and Abomasnow were the only other species to be less than 50% Mega.
Among the "other items", a few were just plain goofy--probably even more than this, but beyond the 10 that get displayed per Pokemon, I have no way of seeing what novelties got tossed into the "All other items" bucket":
There were instances of a Charizard holding Mewtwonite X and Eviolite;
Kangaskhan with Decidium Z;
Mawile with Honey, Max Repel, and even Rage Candy Bar;
Blastoise with a Float Stone (is Grass Knot that big of a problem?) and a Red Card;
Gardevoir with a Beedrillite and a Pearl String (...okay...);
Altaria was all over the place, with Potion, Poke Doll, Revival Herb, Lucky Egg, and Sticky Barb all seeing action;
Sableye with Marshadium Z;
Alakazam with Float Stone (this only cuts 1/3 of the power off Low Kick/Grass Knot, and it's not even weak to either one!);
Manectric with Big Nugget;
Swampert with Water Memory;
Latios with Latiasite;
Heracross with Smoke Ball;
Gallade with a regular old Stick;
Medicham with Moomoo Milk;
Pidgeot with a Kelpsy Berry (I guess it can learn Natural Gift, but then why not Salac instead?);
Glalie with a Repel, and a Strange Souvenir (is that what the kids call Sheer Cold these days?);
Absol with Lucky Egg;
Pinsir with Sticky Barb;
and Abomasnow with Big Mushroom.