Principal Celestia (as this dragon): “I turned myself into a dragon, Luna! Boom! Big reveal! I’m a dragon! What do you think about that? I turned myself into a dragon!” realizes Vice Principal Luna is staring at her “What are you just staring at me for, little sister? I turned myself into a dragon, Luna!”
 
Vice Principal Luna: “And?”
 
Principal Celestia: “And what more do you want tacked onto this? I turned myself into a dragon and 9/11 was an inside job!”
 
Vice Principal Luna: “It was?”
 
Principal Celestia: “Who cares, Luna? Global acts of terrorism happen everyday. Uhh here’s something that’s never happened before: I’m a dragon! I’M DRAGONLESTIA!”
 
Vice Principal Luna: “…”

One merciful day in a peaceful town called Ponyville, countless moments after using her Alicorn magic to turn herself into a young dragon just like Spike, Princess Celestia took a walk around town when suddenly a giant, red-eyed, catastrophic robot known as the Omnidroid begins it’s attack on Ponyville as it overpowers Twilight, Star Swirl, Rockhoof, Spike, Fluttershy, Somnambula, Rainbow Dash, Starlight Glimmer, Applejack, Rarity, Flash Magnus, Princess Cadence, Mistmane, Pinkie, Anon, Sunset Shimmer, Shining Armor, Meadowbrook, Danny, Jake, Megan, Molly and Stygian! Celestia tried to help them out but the mechanical sphere-bodied atrocity spotted the Adult Alicorn Pony-turned-Dragoness child and captured her in it’s devastating claws! The Omnidroid was about to vaporize the tiny white dragon with it’s built-in ray gun but then a magical transformation occurred within Celestia’s pony-turned-dragon body as streams of light began to surround her and glow brighter and brighter, blinding everyone in Ponyville (except the robot)! When the light finally dimmed, THIS happened! Princess Celestia is not a young short little dragon anymore and is now a older tall big dragon with slightly longer arms, extended dragon feet (with brownish purple talons on her toes), tremendous wings, increased fire breath, two large scute-covered boobs and even her Alicorn Princess horn (only lightly and smoothly bent)! This could be the beginning of the Princess’s new dragon lifestyle from magic. Now the severely bruised Mane 8, Pillars of Old Equestria, American Dragon and the Three Humans just stand there and watch as a smack down between the Anthropomorphic Female Dragon of Sunshine and the Gargantuan Killer Robot of Mass-Mayhem rages on!

@mana the immortal  

 
Well, ‘Princess Celestia, Dragon Lord of the Sun’ is the name of one of those disgustingly hard optional video-game bosses if I ever heard one.
 
Those mini-bosses of hers alone probably has some sort of grab attack where they crush any player’s head like a sparrow’s egg.

I imagine she’d have a lot of… fire power… in this form.