Well September's been off to an annoying enough start that I vaguely considered just dumping my old Pyroar-Mega(s) in here, but I resisted that temptation. Let's see if it pays off though. Regardless, congrats to the previous winners:
Lapras-Mega
New Ability: Safe Passage = Whenever this Pokemon successfully uses Surf or a sound move, it switches out, taking halved hazard effects for its ally that is switching in.
Type: Water/Ice
New Stats:
HP: 130
Attack: 085 → 085 (+00)
Defense: 080 → 115 (+35)
Special Attack: 085 → 130 (+45)
Special Defense: 095 → 115 (+20)
Speed: 060 → 060 (+00)
(BST: 535 → 635)
New Moves: Eerie Spell, Healing Wish, and Noble Roar.
Description: "Mega Energy brings to mind its species's brush with extinction, heightening both its sense of loneliness and self-sacrifice. It sings a mournful song constantly."
Gods, I had forgotten how utterly depressing most of poor Lapras's dex entries are given no good deed goes unpunished. They were collective downbeat enough that for a while I considered making it Water/Ghost, but I ultimately didn't go with that just like I didn't go with a Snow/Hail (or Rain...or Perish Body) focus. Instead, as I had also considered from the start, I went with a sound focus mixed with a switching focus to get across the emphasis on it ferrying people without just ripping off Blue Ray's idea for Avalugg-Mega from last slate. Now Lapras-Mega becomes a slow pivot that gets its allies in safely no how many hazards are up at self-sacrificing cost to itself whenever it uses either Surf--get bent, Scald--or any Sound move. As such, it will take a beating if you're too lax about keeping hazards off the field or get greedy against strong mons, especially since it still intentionally has no healing beyond Life Dew and Rest, the former of which is basically a Doubles only move. Even with that intended weakness, it's probably the only mon that can make use of Noble Roar (Parting Shot felt off-flavor)
or Snore
or, given how Galarian Slowking basically never uses it, Eerie Spell, though Heal Bell, Hyper Voice, Perish Song, Sing, and even Growl and Sparkling Aria all work too. (Its ability is simultaneously less impressive and less self-sacrificing in VGC due to hazards pretty much not existing, but a slow pivot that gets something in safely will pretty much always be useful regardless of format, especially when it can use attacking moves to do it. I just didn't want to tie its ability only to Surf while boosting the damage of that since otherwise it would utterly get invalidated by any Water Absorb or Storm Drain mon, which seemed too one-note and unfun.)
Pyroar-Mega
New Ability: Grassy Surge
Type: Fire/Normal
New Stats:
HP: 086
Attack: 068 → 068 (+00)
Defense: 072 → 092 (+20)
Special Attack: 109 → 149 (+40)
Special Defense: 066 → 086 (+20)
Speed: 106 → 126 (+20)
(BST: 507 → 607)
New Moves: Energy Ball, Grassy Terrain, Morning Sun, and Scorching Sands.
Description: "Pyroar-Mega brings both a regal air of arrogance and its grassy hunting grounds with it wherever it stalks as seeks out prey to burn and deafen."
It seems a bit weird to have one of the non-Misty Surge terrain abilities be attached to a mon that isn't even of the type, but Grassy Terrain does fit a real-life lion(ness)'s hunting grounds of the grassy savannahs. Of all the non-Misty Surge terrains, Grassy Terrain also tends to be the most impactful and helpful team player to a (non-HO) team given its healing and its halving of Earthquake's damage. The latter is useful to a Fire mon, mitigating its Ground weakness on the physical side, which having another attacking move that can burn in the form of Scorching Sands helps too. The rest of the new moves play off that as well, and Grass and Ground just so happen to both bully the Rock types would resist its actual STABs even before the pseudo-STAB that Grass now. All this while getting to retain a resistance to U-Turn and thus switch in a bit more aggressively against all the pivoting than an actual Grass mon likely could with Grass's resistance to Volt Switch and Flip Turn. Finally, Grassy Terrain is obviously rather helpful in VGC for most of the same reasons it is in Singles and can be used in conjunction more easily with a Sun setter to power up the Solar Beam that poor, infinitely disappointing Pyroar already has. (I vaguely considered giving it Court Change instead of Morning Sun initially, but it ultimately can't use that better than Cinderace due to shared typing even now with recovery and better speed--4MSS strikes and a lack of item strike again.)
Carbink-Mega
New Ability: Earth Eater
Type: Rock/Fairy
New Stats:
HP: 050
Attack: 050 → 050 (+00)
Defense: 150 → 160 (+10)
Special Attack: 050 → 100 (+50)
Special Defense: 150 → 160 (+10)
Speed: 050 → 080 (+30)
(BST: 500 → 600)
New Moves: Draining Kiss and Heal Bell.
Description: "Its appearance has taken on a haphazard bejeweled one due to its newfound, single-minded persistence in absorbing any minerals and gems it can find. An uneven crown of gems wreathes its head."
Upon Mega Evolving, the Carbink peasants revolt and overthrow the rule of the tyrant, Queen Diancie(-Mega).
Viva communism!
Ahem. Since trying to make the already
oppressed disadvantaged Carbink compete with Diancie-Mega in any way directly feels rather pointless and almost doomed to failure, I decided to instead emphasize the defenses they share that Diance-Mega throws away like the careless aristocrat she is. I didn't want to increase said defenses too much even with the pitiful HP that Carbink and Diancie share, however, given that would make this obnoxious in conjunction with Earth Eater getting rid of a weakness and both of them already having Calm Mind and Iron Defense. I decided to go with Earth Eater in part for the defensive aspect, in part because chemicalmines took Levitate already (grrr), and in part because I've always found it...odd when a mon described as primarily living in the earth or at least spending a lot of time tunneling through it is somehow weak to Earthquake. Given how common Earthquake is in the Pokemon world, there should be a lot more Ghost mons due to that logic, that's all I'm saying.
In VGC, Earth Eater's utility is obvious given that Earthquake is often used there too. Earth Eater also gives this Carbink-Mega a niche of walling Garchomp (as long as it isn't using Iron Head...or Iron Tail) and generally lets it live longer than it should without necessarily having to rely on Draining Kiss backed up by Calm Mind for healing (or, gasp, Rest). While those are doubtless its two strongest options in conjunction with each other (and Earth Power and Power Gem), its other existing moves like Body Press, Iron Defense, Rock Polish, and now Heal Bell mean that it can serve other roles too beyond "Calm Mind cleaner".
As it should be for the revolution.
Hoopa-Mega
New Ability: Wishtwister = Whenever this Pokemon uses a Psychic move or Wish, if any other Pokemon on the field would use a Dark-type move, that move fails and instead deals 1/4 Max HP damage to its user. (Basically inflicts Dark-type Powder temporarily, which seems appropriate to call the pseudo-status Corrupted Wish or something if it needs a name.)
Type: Psychic/Ghost
New Stats:
HP: 080
Attack: 110 → 135 (+25)
Defense: 060 → 080 (+20)
Special Attack: 150 → 160 (+10)
Special Defense: 130 → 140 (+10)
Speed: 070 → 100 (+30)
(BST: 600 → 700)
Weight: 019.8 lbs → 507.1 lbs
New Moves: Teleport and Wish.
Description: "Its confines strain under the surge of Mega Energy, and it seems much heavier despite looking the same. It still smiles constantly, though its mischievousness now has a sinister tone."
Ugh. Despite knowing I wanted anti-Dark ability from the start since Psychic/Ghost
sucks as a typing, I knew there were also going to be issues. Besides Hoopa's already high BST, there was also the catch-22 that giving it an always-on anti-Dark ability would just mean that...people wouldn't use Dark moves against it ever. With this ability, however, it creates the temptation to still try to use Dark type moves against it occasionally since
surely it won't use a Psychic move or Wish this turn...right? So much like a wish, it plays a little game with corrupting would-be desires that blow up in your face and have the djinn still coming out on top despite being confined if you don't guess what you need to do correctly (or, you know, just resist temptation entirely, but shhh).
That said, it says a lot that to maximize this ability, I still had to give a 600 BST mon two new moves despite its already good movepool and despite Psychic having the most status moves--which count for this ability and include Calm Mind, Teleport, and Trick Room--after Normal. I just didn't want it to have to link its Ghost STAB to the ability given that's already a much better STAB than its Psychic STAB normally anyway even before Dark types' total immunity; this especially when its signature move Hyperspace Hole is Psychic type, though that will probably still only be used in Doubles. Its new moves don't really need much explanation, so I'll just end this by saying that its ability is arguably even better in VGC since it also protects its allies from Dark attacks...as long as its allies don't try to use Dark moves themselves. I guess they too will just have to resist the temptation.
Mega Lapras 
Mega Hoopa
Pyroar-Mega 
, 
, 
, 
, 
, 
, 
Psystrike
Sacred Fire
Aeroblast
Precipice Blades (Drought sets up sun)
Origin Pulse (Drizzle sets up rain)
Dragon Ascent (if Mega Hoopa should be brought back in a format using gen 9 mechanics, Ice-types under snow won't have boosted Defense due to Air Lock; I don't think disabling weather for just one attack accomplishes anything else but I could be wrong)
Roar of Time
Spacial Rend
Shadow Force (charge-up period is skipped)
Blue Flare (Turboblaze ignores abilities)
Bolt Strike (Teravolt ignores abilities)
Glaciate
Geomancy (charge-up period is skipped, Hoopa recieves the stat boosts)
Oblivion Wing (Hoopa recieves the healing)
Core Enforcer
Teleport (Cosmog flees the battle before it has the chance to be put back in the 
Sunsteel Strike
Moongeist Beam
Light That Burns the Sky (Neuroforce powers up a super effective hit)
Behemoth Blade (Intrepid Sword boosts Zacian's Attack)
Behemoth Bash
Eternabeam
Glacial Lance (Unnerve prevents Yache Berry)
Astral Barrage (Unnerve prevents Kasib Berry)
Collision Course (also sets sun)
Electro Drift (also sets electric terrain)
effect))
