Rise from your Zacian-themed novelty grave and live again, however briefly!
At least one of these is probably still overpowered or at least, uh, "centralizing", especially given I wasn't sure if we could take away moves, but I'm already making mons for a meta I don't play (again), so shrug.
Mega being Revolved: Mewtwo-Mega-X
New Pokémon Name: Mewacarnis ("mew" + "carnis")
Stats: 120 HP / 125 Atk / 105 Def / 130 SpA / 100 SpD / 150 Spe (+14 / +15 / +15 / -24 / +10 / +20)
Typing:
/
Abilities: Steadfast /
Scrappy (new; hidden ability)
Movepool Additions: Body Press, Iron Defense, Night Slash
Niche: A strong, fast physical attacker with great bulk that gets to repeatedly use its Fighting STAB liberally with Scrappy, not letting Ghosts switch in for free even though like half of them are weak to its other STAB anyway. I begrudgingly gave let it have Night Slash to deal with the Psychic/Ghosts that still resist said Fighting STAB attacks since it's hardly like Ubers has been balanced ever since we were cursed with Groudon-Primal.
(gods, why is this so much better looking than the 3D model? It's the non-diseased-looking forehead, isn't it?)
Mega being Revolved: Mewtwo-Mega-Y
New Pokémon Name: Corruptoo ("corrupt(ion)" + "too" as a pun of typoing "two" due to both being homophones with each other)
Stats: 106 HP / 90 Atk / 090 Def / 160 SpA / 125 SpD / 159 Spe (-00 / -20 / +00 / +06 / +35 / +29)
Typing:
/
Abilities: Insomnia /
Corrosion (new; hidden ability)
Movepool Additions: Sludge Bomb, Sludge Wave, Toxic Spikes
Niche: A stronger, faster, terrifyingly special attack that I wouldn't be surprised if it is rather broken given it still currently has access to Calm Mind in addition to Psystrike and other things unfortunately. I gave it a Poison-typing almost solely because of how much I dislike its visual design; it's easily the Mega I dislike the most on that level. Poison-typing does at least fit thematically as the other type Psychic preys on besides Fighting though, and when it comes practical aspect its additional Poison-typing is at least decent, preventing it from being Poison'd, letting it reasonably have more support in Toxic Spikes, and giving it a quad-resistance to Fighting at least even if the all of the premiere Fighting types in Uber have other ways to physically murder it; it's also a great Geomancy Xerneas check I imagine if that mon is even still a thing.
As for Corrosion, if nothing else it allows this to at least not be basically walled by Steels if it's just relying on its STABs since no-miss Toxic basically screws over all of them. Finally, while Poison is still admittedly such an underwhelming attacking type that it was also chosen for that reason since it's probably the one that Corruptoo can do the least additional damage with as a whole, this mon blows up other Poison mons via its Psychic typing like Eternatus. (The weird Speed is so that Ninjask can pretend it still has worth as Ninjask continues to ignore the existence of Deoxys-Attack and now Regieleki; in all seriousness, I just wanted to be faster than Ghost Calyrex and Pheromosa while adding to its other stats the least.)
Mega being Revolved: Rayquaza-Mega
New Pokémon Name: Deltaray (...was surprisingly not already taken; pun on "delta ray")
Stats: 110 HP / 140 Atk / 120 Def / 140 SpA / 120 SpD / 100 Spe (+05 / -10 / +30 / -10 / +30 / +05)
Typing:
/
Ability: Delta Stream
Movepool Additions: Fusion Bolt, U-Turn, Volt Switch, Wish
Niche: A bulky pivoting mon that may be a bit too obnoxious now that it's Electric/Flying instead of Dragon/Flying (or even just "pure" Flying as I was initially considering). Basically nothing can be as overpowered as the actual Rayquaza-Mega since the main thing that made it so broken (outside of Delta Stream) is that it was the only Mega that could freely use other items, and we have only can add half of the boost it got. That said, in theory something could possibly still be made more
annoying than the current Rayquaza-Mega through type changing and move additions, and this maybe still be that theoretical mon even with trying to hold it back by not giving it Roost or that much added moves-wise. If nothing else, then it's basically the only mon besides Ho-Oh that can somewhat freely switch into the typical Necrozma-Dusk-Mane (assuming that's still used) and basically the only thing that can do so against Ultra-Necrozma-whatever (assuming that still exists). Shrug.