Mega being Revolved: Mega Altaria
New Pokémon Name: Altodracarys
(Altostratus/Altocumulus are types of clouds, while also being a pun on Alto singing)
Type of Pokemon: Evo
Stats: 75/70/90/70/105/80 -> 90/75/90/90/150/60
[+15/+5/+0/+20/+45/-20]
Typing: Dragon/Fairy
Abilities: Pixilate /
Drizzle
Movepool Additions:

Charge Beam, Charm, Gust, Powder Snow, Soak, Wing Attack

Air Slash, Blizzard, Body Press, Boomburst, Muddy Water, Psychic Noise, Sparkling Aria, Thunder, Thunderbolt

Bleakwind Storm, Fickle Beam, Misty Explosion, Misty Terrain, Moonlight, Sandsear Storm, Springtide Storm, Wildbolt Storm
Niche: Storm cloud Altaria becoming the Storm-Bringing evolution. Drizzle and access to all four Storm moves helps give it a lot of coverage and utility. But the big selling point here is Pixilate Boomburst, which will hit non-resists very hard, but will mean it cannot to much damage to anything that resists it thanks to its fairly low Special Attack and low Speed. Maintains access to a lot of utility, such as Cotton Guard + Body Press, allowing it to act as a solid defensive choice with good offensive options.
Mega being Revolved: Mega Ampharos
New Pokémon Name: Mjolnilamb
(Mjolnir, hammer of Thor)
Type of Pokemon: Evo
Stats: 90/75/85/115/90/55 -> 120/120/90/75/90/60
[+30/+45/+5/-40/+0/+5]
Typing: Electric/
Fairy
Abilities:
Cotton Down /
Teravolt
Movepool Additions:

Baby-Doll Eyes, Draining Kiss, Nuzzle, Parabolic Charge, Spark, Zing Zap

Body Press, Earthquake, Rising Voltage, Tail Glow, Tail Slap, Thunderclap, Volt Tackle

Alluring Voice, Aqua Tail, Fire Lash, Misty Terrain, Moonblast, Moonlight, Play Rough, Power Whip
Niche: I removed Fairy from Audino, so it is only fair I give it to someone else. After all, we will have a lot more Mega Dragons down the line, and not nearly as many Fairies. Fairy also pairs well with the design moreso than Dragon I would argue. Finally, Tail Glow on the Pokemon that has had a glowing tail since it was introduced. The base form benefits from Tail Glow and Thunderclap, but the evolution will be a physical attacker that still has access to a STAB priority move if it so desires. A Physical Electric/Fairy is something the format does not have, as Tapu Koko is normally a Special Attacker. Gets a lot of Tail and Tail-adjacent attacking moves to give it more tools to work with.
Mega being Revolved: Mega Audino
New Pokémon Name: Doctrspectr
Type of Pokemon: Evo
Stats: 103/60/86/60/86/50 -> 123/84/96/84/96/42
[+20/+24/+10/+24/+10/-8]
Typing: Normal/
Ghost
Abilities: Healer / Regenerator /
Cursed Body
Movepool Additions:

Astonish, Cosmic Power, Dizzy Punch, Follow Me, Headbutt, Hypnosis, Milk Drink, Mimic, Natural Gift, Psychic Noise, Purify, Quick Attack, Recycle, Rock Climb, Stored Power, Weather Ball

Beat Up, Destiny Bond, Dream Eater, Embargo, Fake Out, Foul Play, Hex, Leech Life, Memento, Nasty Plot, Nightmare, Ominous Wind, Parting Shot, Poltergeist, Shadow Punch, Shadow Sneak, Spectral Thief, Sucker Punch, Switcheroo, Taunt, Thief, Torment, Trump Card, Will-O-Wisp
Niche: Not only does the base form get Eviolite Regen which is already great, but now the evolution has this uncommon typing paired with Regenerator. This new form instead takes the doctor inspiration of the base form and evolves into a form of mad scientist with all of the new tools at its disposal. Most of the moves above are likely to be just for flavour, but a lot of these would prove to be quite useful, such as Milk Drink, Spectral Thief, and Parting Shot.
Mega being Revolved: Mega Lopunny
New Pokémon Name: Jumpinjak
(Jump + jackrabbit + jumping jacks)
Type of Pokemon: Evo
Stats: 65/76/84/54/96/105 -> 84/108/84/60/96/108
[+19/+32/+0/+6/+0/+3]
Typing: Normal/Fighting
Abilities: Cute Charm / Scrappy / Limber
Movepool Additions:

Follow Me, Knock Off, Play Nice, Nature Power

Body Slam, Double-Edge, Karate Chop, Mach Punch, Quick Guard, Stomp, Superpower, Wake-Up Slap

Axe Kick, Blaze Kick, Bulk Up, Final Gambit, Smelling Salts, Submission, Trop Kick, Victory Dance, Vital Throw
Niche: Was considering making this just a diet Mega Lopunny. But now with this stat spread I realized I could give it the best Fighting move it could ask for: Victory Dance. With Attack and Speed below 110, they are both comparable to those of Hisuian Lilligant, but in exchange it gets more bulk to work with.