@Antonyourknee  
I was talking only about Sombra. Well, while you raise completely logical points, Sombra can take all four princesses as consorts after he has ‘‘defused’’ them. Plus, a story like that could make for intersting fanficton.

@Background Pony #B6F4  
Many reasons  
1.Sunsets shimmer is female and hates Celestia and probably Twilight(did EQG happen in this pic?, I’m gonna say not in my particular headcannon and she probably just hid from Celestia for a couple years and by fate met sombra)and since theirs no way Cadence and Luna would let this go,she probably needs to kill them too along with most of the higher echelons of equestrian leaderhship.  
2 Sombras a ghost or a magical metaphysical apparition or he’s just too power hungry to care about that kind of power unless you think he would go really grimdark. Maybe I suppose it wouldn’t be out of his character and I did kindle imply he would try to control sunset as well,  
3 when fighting god like enemy’s who have many thousands of years of experience and mysterious power on hand(hoof)it probably just best to completely destroy them lest they remanifest somehow and come back years later and try to kill you in one of their revenge schemes or something like that,that’s what Sombra did didn’t he?.  
4 if they did keep them as consorts ,he would need to like break their minds or something to make sure they don’t try to rebel or lead the people against him,in fact he would need to either break the minds of most of the populace to ensure complacency or shock them into submission by killing their leaders in front of them.

@Antonyourknee  
Why kill the princesses when you can keep them as consorts?

Damn double uploads!

@Background Pony #92A3  
“Foolish mare,when you were not even a thought of drunken lust by your inbred ancestors,I already reigned over the mightiest Imperial Empire on Equis and bound the unholy dark powers of crystalic obscuration to my will.
 
 
Only when those who claim bearing over the sun and moon grew their spines and combined their powers against me then was I defeated but not killed!For despite their best efforts otherwise not only had I survived but I cursed my realm to a millennial slumber with me.And when I returned,not only did I Cripple the captain of the Equestrian royal guard and outwit the prized protégée of the Sun nag with traps laid a thousand years in advance but I also survived a direct blast of weponized magic designed to completely annihilate beings like me.
 
So yes mare…I am dead.But even thought I no longer tread this plain of existence I know of fear-based magic so terrible that I could rip your mortal mind to shreads and leave you a sobbing,mad,husk of a pony for the rest of your miserable life and beyond even that….
 
So listen up mare….you best disregard any former notions of power or glory that you had because you will go to a cavern in the north,there lies a cult of shadow worshipers loyal to me.Once there I will evaluate your potential,see if You can even compare to the pony that is your replacement in the sun court,and if I deem you worthy I will teach you such spells and skills that the greatest Archmages in the sisters kingdom will seem but worthless street illusionist in comparison. And then when we are done,we will march to Canterlot,declare our glory,and you will kill those four mockeries of pony that dare to label themselves with a royal title.And when the sun falls,our shadow will cover all the lands of Eqius. Sunset shimmer this world and all those like it.will.be.ours(MINE!)”

@Background Pony #92A3  
“Foolish mare! When you were not even a thought of drunken lust between your inbred ancestors,I had already reigned over the migthest Imperial power on Equis and had bound the darkest unholy powers of crystalic obscuration to my will.
 
Only when the duo goddesses of the sun and moon combined their strength against me was I defeated but despite their best attempts otherwise I had not only survived but cursed my realm to a millennial slumber with me and when I retuned,not only did I cripple the captain of Equestrian royal guard with ease and outwit the prized protege of the sun nag with traps laid a millennium in Advance but I also survived a direct blast from a magic designed to destroy a being like me.
 
So yes mare.I may no longer tread this plane of existence physically but even in this form With my fear incantations I could rip your mortal mind to shreds so great that you would be reduced to a mad,sobbing ,wreck of a pony for the rest of your miserable life.
 
So disregard whatever pathetic notions of power and greatness that still cling to your deluded mind and listen up.You will travel to a cavern not far from here where a few of my loyal minions still reside ,there I will observe your potential, to see what the sun nag thought resided within you,and if I deem you worthy to even learn under my name,I will teach you such power and magic that the most powerful archmages in Celsetias kingdom would be rendered mere magical tricksters in comparison and then when you and I are done we will march to Canterlot,declare our glory and then you will kill those mockeries of Equine form who dare to label themselves with a royal title, and when the sun falls the whole world will be cast in our shadow sunset shimmer,this world and more like it will be ours(MINE)!”

“You know the difference between me and you? You’re dead.”

Alternate Title: “Let’s Conquer Equestria, You Jerk!”

@PonyPon  
He could also be a former Captain of the Royal Guard. Basically, Shining Armor only infinite times better.

@Background Pony #B6F4  
Who says he can’t do both?

@Trickquestion  
I always thought that Sombra was a Mercenary Blood Knight.

About time someone drew these two together.

And then they argue over who gets first choice of slaves.

I already headcanon the idea that Sombra was Celestia’s student, so this is great.

There’s a team up I’d love to see.  
Gives off a very Sith-like “Rule of Two”: One to embody power and one to desire it.