All recommendations for characters to be featured in a Multiquestria story should be submitted here.

Rules for child characters

1. If the character has a defined age, they should be at most a young adult. (exception: long-lived characters such as the Chrysalis and the Princesses can be paired with older characters)
2. If the character doesn't have a defined age, they should be able to physically grow. (for example Mario and Luigi, who don't have any canon ages but due to their baby forms are physically able to)
3. Character must have a canon appearance and personality to work with.

Rules for parent characters

1. Character must be an adult by the time of the series premiere.
2. Character must have appearances beyond the comics/novels that clearly establish their character (with the exceptions of Sombra and Radiant Hope, whose comics I have read).
3. I need to like the character.

Rules for origin worlds

1. No worlds primarily focused on horror, apocalypses of any kind, or war stories.
2. No already used worlds unless I really like the possible dynamics.
3. Worlds need to have some reason for the ponies to not totally break the system during the return home arcs (i.e. no worlds totally devoid of magic).
4. I need to either have knowledge of the worlds or be able to learn about them with relative ease.
5. Equestria Girls and the alternate worlds established in the comics are ineligible because that would be boring.

All confirmed pairings

1. Sonic the Hedgehog, son of Rainbow Dash in Super Sonic Rainboom
2. Dipper and Mabel Pines, children of Bright Mac and Pear Butter in Pine Apples
3. Toothless, son of Dragon Lord Ember in Fury of the Dragon Lord
4. Link, son of Daring Do in Daring Do and the Blade of Evil's Bane
5. Flayn, daughter of Princess Celestia in Celestial Saint

All rejected pairings

None so far.

OH, I think a good pairing would be Akko from Little Witch Academia being raised by Trixie (both adore stage magic and struggle doing real magic, and while Akko is certainly more humble then Trixie that might be a good thing to help Trixie out, similar to how Rainbow's ego seems to have settled a bit thanks to Sonic)

And just putting it out there to see if you like the idea, Lightning Dust raising Shadow the Hedgehog, Rainbow's rival with one of Sonic's most iconic rivals

Oh and since I saw you had a folder dedicated to Equestria royalty I thought of a few new ones

Celestia raising Vegeta (Prince of All Saiyans with the Princess of Ponies, and just an idea as to how it happened, during the Saiyan Saga Roshi tries to use the Evil Containment Wave on him, only to have something go wrong sending him to MLP or for strictly magic perhaps the Wizard Babidi tries to send him somewhere to better control him, and his spell gets screwed up by Dabura)

Luna raising Inuyasha (I don't know, just something about the fact that he loses his powers during a new moon would resonate with Luna)

Finally for the villians

Chrysalis raising Kars from JoJo's Bizarre Adventure (both are similar in their villainy being of a parasitic species and wanting to dominate and rule)

I might come up with a few more ideas later, just let me know if I reach a limit of some kind and you don't want to post more (of if you end up changing the rules in some way)