I’m genuinely so obsessed with my dsmp x mlp AU. So here’s me refining some things:
Karl: to me, Karl is a changeling. He is already so bright and colourful, and chalked full of love, so what could be better for him. I’d like to think he left to Ponyville because despite the fact that he loved the hive, he wanted to meet new people and spread more love! He is pretty much always seen in his pony disguise, and his friends are originally unaware of the fact he even is a changeling (inspired by Karl’s ‘gummy form’ ofc, and the fact he is often depicted as being able to switch between the two, although typically presenting as human). I also think that he often changes the colour palette of his changeling form! And his pony form cutie mark would be the classic square shaped spiral he uses. In his pass time he loves to journal (as well as read romance novels which may or may not have been one of the things inspiring him to move, I definitely see Karl as a bit of a hopeless romantic, greedy bastard with two boyfriends).
Sapnap: I am 1000% sure he is a kirin. Sapnap is my favoruite, so he is getting my favourite mlp creature. I am genuinely so sad the kirin only appear in like one episode (I highly recommend looking up the kirin so get a better understanding, once you read it I’m sure you’ll realize why I chose Sapnap for it). I think the little dork probably got lost as a kid and while wandering stumbled upon Bad, who ended up taking him in! He ends up meeting Dream and George and begins sneaking off with them on adventures. Bad is a bit afraid something would happen since Sapnap has a temper and when a kirin gets mad it turns into a nirik, which could very quickly become a threat to others. That is why he doesn’t really want Sapnap to go out too much, especially without his knowledge. But of course he does it anyways.
Quackity: I was considering making Quackity a hippogriff but I honestly think pegasus would work just as well - I like pegasus because it’s just more simplistic and classic, it works well and helps keep the au a bit more grounded in the core three of mlp - but also hippogriffs are a bit more bird-like and semi aquatic, like ducks are (and I wouldn’t have to give him a cutie mark) - so I’m kinda stuck between the two. (I’m leaning a bit more towards pegasus though because of this:) Quackity is in a similar situation to Scootaloo, where he can’t really fly despite having wings, so he covers them up with that one blue jacket he always wears 😭.