How powerful is Discord?

Low level reality warping - Turning clouds into cotton candy which rains chocolate milk. Changing animal biology like giving deer legs to rabbits, and making pigs fly. He can both create objects out of thin air(etc a bullseye dartboard) as well as change the properties of objects(etc turn a normal glass of chocolate milk into a grenade).

High level reality warping - Turn buildings into paper. Changing the environment on a planetary scale drastically, etc turning roads into soap, messing up gravity, screwing up world physics itself(food will be spat out instead of being eaten), and changing the personalities of every inhabitant of a town(likely the entire world actually, but we never saw the effects elsewhere). Controlling the sun and the moon casually. In short...total chaos, as befits his name.

Teleportation - Limits not shown, but he's pretty much able to teleport anywhere and anyplace, even highly protected ones like Canterlot castle.

Limited time travel - He was able to teleport himself and a pony to witness an event several hours ago, however, he is unlikely to be able to interact with the past, as the characters from the past showed no reaction to his presence, and he would have used this ability to prevent his own defeat.

Illusions - He can turn himself into random objects like being part of a stained glass, or a balloon. He's also able to project illusions of other objects like talking apples, making a boulder look like a huge diamond, or even making a small cloud look like a city. His illusions are so real that his targets will ignore all else, and believe nothing but the "truth" of the illusions. He can give voice to his illusions, or project an omnidirectional voice to confuse his opponents. Lastly, he can also plant an illusion of a false future in a character's mind to mislead them.

High level telekinesis/gravity manipulation - He was able to levitate multiple large objects casually, as well as ponies who were fighting against him(but Twilight Sparkle was able to use her own magic to repel his telekinesis).

High level magic - He was able to easily bypass all of Celestia's magical defences as well as Canterlot's defences to steal the Elements of Harmony without her knowledge. He was also able to remove the Mane Six's wings and horns casually to limit their abilities.

Mind control of sorts - Discord is able to change or reverse a character's personality either through mind-*vulgarity*ery or touching them. It should be noted that although he never interacted with Big Macintosh, he managed to switch his mind with a dog's, implying his level of mind switch/control is very high.

Immortal - It is shown that Discord is apparently immortal, as he ruled the planet without fear, and was only defeated with the Elements of Harmony, which are the most powerful weapons in MLPverse. Also, he was turned into stone for 1000 years, and was freed later with no apparent side effects.

Cosmic awareness - Despite having never interacted with the Mane Six, Discord was able to accurately point out all of their strengths and weaknesses. He also knows where they live, and what it takes to break his enemies down mentally.

Genius intellect - Discord is a chaotic evil genius. He's able to trick and manipulate characters into doing things they wouldn't thought possible(with the exception of Fluttershy whom he underestimated). He also plans ahead, and is quick to remove any potential danger to himself.

Lastly, it should be noted his powers are even greater than that of Celestia, who's the goddess of all ponies. She can control the sun and the moon, and has the greatest magic power amongst all ponies. She is able to solo HST.

The only characters shown thus far who can pose even the slightest challenge to Discord due to their own magic prowess are Celestia, Luna and Twilight, and that is only in the magic department. Once he starts using his other abilities, he is pretty much unmatched.