The Legends: Arceus reinvigorating the series, and part of this is due to the creativity in reinventing older creatures.
With the roster count approaching the 1,000 mark, working in Regional Forms for existing Pokémon creates a great balance so Game Freak doesn't have to release 100+ new ones every generation. Given the love past games have brought to previous species, there are undoubtedly others who deserve the same level of affection.
Druddigon
Though its somewhat jarring color scheme was offputting stylistically to some fans, Druddigon is arguably one of the most underrated Unova Pokémon. The single-stage Dragon-Type creature has respectable Physical Attack and Physical Defense stats, but it's ittedly outclassed by stronger alternatives in its native region (i.e. Haxorus, Hydreigon).
It could certainly make do with a new evolution, but its fairly complete-looking design could justify an alternate form too. Preferably, a new form would give it an artistic makeover and add a dual typing that complements its Physical offenses or converts Druddigon into a Special Attack/Defense tank.
Absol
Getting rid of fan-favorite features became a tired trope of the Pokémon games, and Mega Evolutions were among them. The Hoenn region-native Absol did get a shot at a reinvention with one but could make a case for getting a Regional Form in Scarlet and Violet, namely for how long ago its Mega Evolution came and being (mostly) inaccessible in modern games.
The lore behind Absol was that it was misunderstood as an omen that causes catastrophes when in reality it's warning people against natural disasters. Perhaps a Fairy-Type variant could play on this fantastical backstory of the Pokémon.
Mightyena
The Poochyena line is an early-route pair of Pokémon that's unfortunately been neglected after the 4th generation -- and the 3DS remakes that came years later. They're charming, sleek hyena-inspired designs with a welcome dose of dark edginess to complement their typing, but their battle prowess doesn't match.
These games are generally easy, but fans online have mentioned that Mightyena eventually gets deposited in the Pokémon Center as the story progresses. Giving these two, and Mightyena most importantly, a Regional Form would be a great way to make it relevant again with a visual revamp and a boost to its currently subpar stats akin to the Zigzagoon line.
Nidoking
The original Kanto region predictably gave many longtime fans memorable Pokémon, and both of the Nidoran lines are among them. Nidoking is also one of the strongest dual-type Poison Pokémon thanks to the coverage it provides with the Ground-Type and has a great, imposing character design to complement it.
When the Regional Forms mechanic was introduced in Sun and Moon on the 3DS, some fans expected him to be a shoo-in for an Alolan Form since the games were specifically overhauling Kanto species. Getting one in Scarlet and Violet would be better late than never, and could swap Ground for Fighting if Game Freak wanted to keep its Physical assets.
Nidoqueen
Should Nidoking get a Regional Form in the 9th generation, Nidoqueen is practically required at that point as well. She also skews more toward Physical Attack and Defense, however, Nidoqueen's stats fall a bit lower than Nidoking. Like the male counterpart, she could also receive a Poison/Fighting dual typing or gain something new altogether.
A good way to differentiate from Nidoking could also be to become a Special Attack-oriented battler along with a new creature design. This duo is one of the most iconic ones for veteran players of the Kanto games, so it'd be great to see Game Freak give them a makeover since Regional Forms seem to be a mainstay mechanic.
Arbok
Thanks to the anime having one as Jessie's signature, Arbok is another recognizable Pokémon for the franchise. But even with that recognition from the classic days, it's still arguably one of the more underrated Pokémon from the Kanto region.
It's a simple yet effective cobra-inspired design with a fitting Poison typing but doesn't leave much of an impression in battle. Since the Ekans line is comprised of two stages, it could justify a new evolution as well. However, from a design perspective, a regional alternative could also suffice, with popular fan mockups since the Alolan generation of games favoring an aquatic version.
Flygon
Flygon is a classic example of a fan-favorite Pokémon that's been bafflingly neglected once variant form concepts like Mega Evolutions and Regional Forms were introduced into the mainline games. The Dragon/Ground-Type was one of the more easily accessible dragons of the Hoenn region, and it had hefty strength for not being a Pseudo-Legendary species.
Fans have been clamoring and making up their own redesigns since Mega Evolutions during the X and Y days, so a Regional Form in Scarlet and Violet would be a great compromise for longtime fans.
Feraligatr
Legends: Arceus gave Johto starter Typhlosion a Hisuian Form that bolstered the Pokémon's prominence among fans, so there's no reason the likes of Feraligatr shouldn't get the same treatment soon. The starters getting makeovers in Game Freak's latest endeavor was particularly welcome, as many fans were growing tired of the Kanto region getting pandered to.
Now that the other starters seem like fair game, another fan-favorite like Feraligatr could take advantage of the Spanish-inspired generation. Johto arguably had some of the most consistently well-designed starters, but Feraligatr and Typhlosion were the most competent in battle.
Eevee
While Eevee has gotten plenty of attention since the franchise's inception in 1996 onward, getting a Regional Form specifically would be an interesting twist. The Normal-Type Pokémon has gotten eight unique evolutions over the years, each having a different typing.
But giving Eevee a regional form that changes its design and drops the Normal-Type -- or at least becomes a dual Normal-Type -- could pave the way for a more intriguing evolution. Fans would get a fresh new take on the creature while also getting a new evolution for the first time since 2013. Eevee has a fun gimmick as is, but this would be a special way to add a new layer to it.
Meganium
Though Meganium isn't the most popular of the Johto trio of starter Pokémon, that's mostly due to its weaknesses in battle when stacked up against the challenges Gold, Silver, and Crystal pose. That's exactly why it should get a variation in Scarlet and Violet, as it'd essentially be giving the Grass-Type a new lease on life.
It would also be a good opportunity to complete a Johto trio of regional variations, with Typhlosion bringing this a third of the way there. Being a monotype Grass Pokémon could hypothetically allow for plenty of creative liberty on Game Freak's part, too.
