Darkest nightmare night nr: 31.  
Absorbing all the darkness in Ponyville does strange things to your body. Someting that the pony of shadows had to learn as they attempted to flex their power.
 
 
The pony of shadows had always been a big pony. Towering over lessers like a force of nature. It had been an easy solution when there had only been two minds inside. Now. As the moon-bound nightmares came rushing in All that power quickly overwhelmed the meager enquine shape. It was not so much torn appart as outgrowing its own anatomy as all the power of the nightmares puched out from within. The muscles and were puched out of place, dissolved and reformed into new chapes. The bones lost their solidety and the marrow inside was transformed into the thickest, blackest tar of solid darkness.  
The part of the colective consiousness previously knows as Stygian, Whos boddy formed the base for this creature of shadow, felt weirded out by all the changes. It was easy to drown in the colective mind of hundreds, maybe thousands of shadows that now made upp this entity they were becoming. A thousand minds and a tousand memmories, all with different states of being, all unfamiliar with the mortal shell. And their unfamiliarity only added to the weirdness as they all felt it as one.  
But Shadow, the primary force in the symbiotic bond that, with Stygian formed the Pony of shadows, assured the part known as stygian that they, as hosts, would sit at the top of the colective hivemind. Ruling the boddy like kings while all the other enteties took up places in its functions. Becoming one with the flesh and bones they had so longed for. Each adding their power to the coctail, strengethening each other and the whole.  
Each a nightmare in their own right. All with their own shapes ans sizes. The massing collection of shapes now forming a melting pot in the colective hive mind. Forming av ever unclearer image of shape. A shamble of shadows. Yes, thats what they were. Formless, shapeless, yet ever growing as all that nightmare power worked the body into a thousand different new shapes.
 
From an outsider’s perspective. All the voices coming out of the growing shadow carried the same dark tone, and made it impossible to tell if the creature was talking to itself - or making statements to its opponent in this growth-off. Either way, it added to the spook factor. And certainly made the mighty Spikezilla nervous.
 
Meanwhile. Nightmare Rarity just though: “Those silly boys. Always going around mutating their bodied beyond recognition and making dark pacts just to impress a girl … Or worse – Each other.”