This wasn´t what Discord had planned at all. He simply didn´t quite comprehend the forces he was playing with. Of course, he obtained the result the yearned for, right? But at what cost?  
After Tirek´s fall and Discord´s redemption he, the master of chaos and mayhem has utterly confused. How somepony could have forgiven him after having already being offered a chance for redemption? He had turned the world upside down, destroyed Equestria´s sanity, disrupted Twilight´s friends and submitted her to the sadistic torture of contemplating everything she had ever loved being burnt to ashes for his sole rejoice. He had been punished, obviously. And then, Celestia held a caring hoof to him, allowing him to be reformed. He had mocked such proposition and deliberately attempted to ruin it, and still, his new and only friend never gave up on him. Despite his numerous flaws, she still cared about him and treated him as an equal. And at the first opportunity he obtain to restore his domain upon the land, now by the side of someone who he could now discern as a manipulative trickster, he took it. He forgot all they had done for him and exchanged a convenient friendship for the power he once possessed. And when it backfired as he should have predicted, something snapped inside Discord. He saw the result of his actions, how befriending evil had resulted in his fall along all he once loved, the same way he orchestrated Equestria´s some time before. He thought everything was lost. He thought that the death that Tirek would bestow him would be a deserved retribution and, in part, liberating. He decided not to present any resistance and assuming his fate. And then, as the angel she was, Twilight freed him from Tirek´s grasp. For no other reason than charity. She could have left him to die; she wouldn´t be losing something important or beloved. Yet still she thought that his days were not over yet. And as reward for that uninterested feat, Tirek was defeated.
 
Day after day Discord could not find a reasonable way to explain why Twilight had saved him. He did not ever ask, of course. After all, he was still the impassible Discord, he whom had contemplated the beginning of time without being perturbed. And yet, the decision of a mere mortal had been enough to disrupt his vision of life. He needed to thank her, to demonstrate how profoundly grateful he was. But his own pride and self oppose to do so. He would always be the god of chaos, and nothing would change that. Or would it?  
In his desperation, Discord lucubrated a plan in order to be of Twilight´s liking. He was too blind to see that she had saved him no matter how he was, and there lays the tragedy of this sad tale. Twilight was a being of order, probably to most ordered pony he had ever met. Even to a sick and disturbing level. If she wanted to properly thank her for her actions, he had to become what she loved the most. He needed to be order.  
It was only gratitude, after all. Once simple way to prove how far he was willing to get in order to show his regret.  
Discording other ponies had been a hobby of his for so long he did not even remembered it. Could that be applied to himself too? He soon realized that it was truly possible.  
Being his own opposite should be proof enough for her. But he did not take in consideration the pain. It was an unprecedented dolor, much more intense than anything he had ever experienced. The sensation resembled to what he had felt when Tirek detached him of his magic, but much worse. He did not sense how something was taken out, no, he felt as something burned him from the insides of his chest, inexorably extending through every nerve, every shred of skin. Consuming it, replacing every cell of it with something horribly new. Soon, the burning sensation became visible as a blinding brightness radiated form the old body. His very eyes were a window to the energy he had so negligibly convoked. Suddenly, the harmful energy was eclipsed by the crunch of his own bones, as they metamorphosed into something different. Or, would it more correct saying, something equal? Soon, his disharmonious limbs adopted a unique and only form, a combination of the claws and feet he had always had.  
As the horror of this transformation began to end, Discord tried to ask for help, but instead of words what abandoned his lips was a dense and dark substance, resembling to blood. But it was not blood, it was not something as mundane as a mere corporal fluid. His very soul was bleeding.
 
And finally, with the liquid slipping by his chew, slowly yet firmly dyeing his coat, as who he had always been, who he was, and who he was destined to be became a distant memory, all Discord was capable of uttering was a sole murmur:
 
“Something feels… wrong.”

Maybe the Tree of Harmony messed with Discords magic when it gave it back.

now though i cant help but picture a separate discord off to the side with lion forelegs, goat hooves, bat wings and twisted ibex horns

is this what twilight’s ‘reforming’ spells would have done to him had he not eaten them?

My first thought:  

@PonyPon  
worse… He’s IN ORDER

Oh my goodness.
 
 
He’s symmetrical!