so… sombra and svengallop. lets start from the beginning hfsjh  
first things first, sombra didn’t die. the blast that killed him in the show only stripped him of all his magic in this au. he’s left looking like a normal unicorn, although he doesnt even have unicorn-level magic left in him. twilight is given the task of dealing with him, which doesn’t entail sticking him Ultra Jail since he’s essentially harmless in this state. instead, she places a spell on him which will keep him locked in ponyville (to keep an eye on him) and she gives him a simple home to live in.
 
sombra is understandably frustrated. he’s always been used to living life as essentially an untouchable god - lavish surroundings and ponies to do his bidding at every moment. now he has to do things like… go grocery shopping?? what is this?? he quickly becomes essentially depressed, staying inside at most times. he doesnt feel like trying to make small talk with these annoying ponies surrounding him, especially since they’re all afraid of him anyways (not that hes complaining - anything that makes him feel a bit more powerful is welcome).  
twilight resigns herself to checking up on him every now and again, although she treats him like the criminal and would-be villain he is. he actually becomes a bit dependent on her since he doesnt understand a lot of new technology (oh yeah, regular real-world tech exists here lol) or even how to properly buy something. he usually uses his intimidation to get what he wants, though, even after she explains it to him. of course, this being the pony who put him into this whole mess, he antagonizes her at every opportunity possible.
 
its like this for a healthy amount of months until he finally caves in and starts going out. when he does, its always to a bar of some sort. he drinks a lot to try and forget what kind of nightmare hes found himself in. its during one of these nights that he meets svengallop. sven spots him, looks him up and down, and says to himself “i can tap that”. i mean, he KNOWS who king sombra is, he knows how powerful he used to be and how everyone else finds him terrifying. in fact, the bar-goers are usually situated so that no one has to be within 10 feet of the guy. but sven walks right up to him, offers him a drink (not that he doesnt get them for free already) and eventually gets him to take him home.
 
that night was so good that sombra demanded they see each other again. and again… and again, until it was a regular Thing. they werent really dating at all, there were no emotions involved beyond “im bored and need someone to take out my frustrations with”. sombra knew how obnoxious sven was and sven knew better than to mess with someone who once enslaved an entire empire, and yet…
 
well, at some point sombra started feeling… off. he was feeling things a lot more intensely than before, and often got dizzy or nauseated. he knew something was wrong, so he sauntered up to twilights castle and started bugging her about it. he listed off his symptoms and eventually it dawned on twilight that he was pregnant. sombra was like um??? no??? im definitely not lol what the hell do you mean. she asked if he was sexually active and yeah, he was, but its not like a pony could get an umbrum pregnant right? twilight knew she was right but let him live in denial for a while longer until he started showing and he couldnt pretend it was just mega food poisoning or something anymore.
 
so, he was pregnant. okay… what now? he and sven had still been having their frequent hookups but eventually sombra started saying no to drinks and sven was tipped off to something being different. sombra was forced to admit what had happened and sven just lost it. they had a huge argument that lead to sven leaving and ghosting sombra for the entire pregnancy. sombra, left with his heightened emotions and all alone, had to deal with all of it himself. twilight offered what she could, but this was sombra we’re talking about. she didnt want to get too involved with a guy like that and his issues.  
sombra eventually had the kid and when red velvet came into the world he just knew he was gonna be wrecked. immediately he felt an intense fatherly instinct towards her. he sent a picture to sven as one last final attempt to get him to understand the gravity of the situation, and it actually worked. sven couldnt deny that she was cute. he traveled over to ponyville for the first time in months to see his newborn daughter.  
sven stuck around for a while to patch things up with sombra, but eventually he had to be off again for work. sven would leave for weeks at a time, return for a few days, then repeat the cycle over and over, only sticking around for longer (at most a month) on off-seasons. sombra for the longest time lived as mostly a single father, only getting financial support from sven. this lead to red velvet calling sombra “dad” and sven “sven” which sven resents to this day.  
sombra and sven had a lot of arguments about all of this, and while they ended up getting closer and actually dating for most of red velvets childhood, they also broke up several times, sometimes for months at a time. it took years for either of them to even feel any love towards the other at all, but eventually it did happen. it might be hard to see what either of them see in each other, but the heart wants what it wants, i guess.  
it takes so much longer for them to actually settle down and stop hating each other most of the time. red velvet is affected by this, but sombra was a surprisingly effective father to her. she’ll say he did the absolute best with what he had and that he always cared for her more than anything in the world.
 
when she does eventually move out, its devastating to him. he immediately asks sven to have another kid, and although it takes some convincing… well, thats for another time hgfjfs  
there is genuinely so much more i couldnt even say here. i know this is the longest thing ever written but trust me… theres so much more. me and connor cant STOP talking about these two.expect a lot more to be made concerning this au - svenbra, the next gen mane 6, the original mane 6, maybe some of the other pairings… god, its bonkers, guys.i hope you like this cuz ur gonna see a lot more of it u___u