I just really wanted to redraw this pic. It bothered me~
 
***  
[Knocks sound on the door]
 
Twilight: Hm? I wonder who that is?
 
Spike: You want me to get it.
 
Twilight: I’ve got it. [opens door] Good afternoon, how ar…Uh~
 
Spike: Who is it, Twi?
 
Twilight: Uh…
 
Sombra: Good afternoon, Princess. This king pray that this day finds you well?
 
Twilight: …
 
Sombra: As for my presence here this day, I have come because of your summons.
 
Twilight: Summons?
 
Sombra: [Reaches into saddlebags, ignoring Twilight’s nervous step back as he pulled out a sheet of parchment.] This.
 
Twilight: You mean-
 
Sombra: This king wishes to apply for employment. May I come in?
 

 
Sombra needs a job.
 
He’s a fairly traditional guy, wanting to support his spouses and keep a roof over their head. Sure, Fluttershy and Iron don’t need the help but Sombra gets… not bored cause that’s what common ponies feel. He feels restless when he isn’t doing anything. As such, he went out to look for a job. As you can imagine, being a depowered former dictator who oozes evil intent isn’t the best starting point when looking for a job.
 
Then he spotted Twilight’s flier.
 
Despite his looks, Sombra is very well-read, knowing many dead languages and dialects. He isn’t as much a book worm as Twi but would prefer being a librarian than to be a cashier at a 7/11. Sombra gets the job though having to treat spike as his senior rubs him all the wrong ways. His time spent working at the library also helps him integrate into Ponyville, though many ponies still fear and avoid him outside the castle.
 
Note: This takes place before his surprise pregnancy. During that time, he takes a break to give birth and take care of the children as a househusband. After his kids get old enough, he goes back to work, having his children stay with him after school. It’s chaos.