Trixie

Trixie (often referring to herself as The Great and Powerful Trixie) is a Unicorn pony and traveling magician who appeared so far only in Boast Busters. She visited Ponyville with her show, in which she greatly exaggerates her abilities and shows off with the addition of fireworks, going so far as (falsely) claiming to have defeated an Ursa Major to save Hoofington.

Personality
Trixie has a very theatrical personality and constantly speaks in an overdramatic manner, often posing or setting off fireworks to complete the effect. She is extremely confident in herself, handling the main characters' heckling like it was part of the show and returning to her haughty tone even after being shown to be powerless against the Ursa Minor. In her defense she also showed a fair amount of courage in standing up to it in the first place, along with admitting that it was an opponent far beyond her (which was the only time she dropped her 'Great and Powerful Trixie' persona and spoke normally). These good qualities admitted however, her constant boasting and over-the-top humiliating of her hecklers alienates the other ponies.

Powers
While not coming close to living up to her claims, Trixie's magic is still rather exceptional among Unicorn ponies. It is not, however, as powerful as Twilight Sparkle's. It is assumed that as all unicorn ponies' powers are based on a unique talent, Trixie's magic manifests as parlor tricks and other illusions. She also shows quite subtle control of her telekinesis with her rope trick and created a whirlwind from a rainbow to incapacitate Rainbow Dash. In her fight with the Ursa Minor she showed the ability to produce lightning from a cloud she had created, which left a prominent burn mark on the beast (which only served to annoy it unfortunately).

History
In Boast Busters, Trixie arrives in Ponyville, having been rumored to be 'the most magical unicorn in all of Equestria.' At her show, Trixie boasts about her great magical abilities. She then claims that she has vanquished an Ursa Major, an enormous bear creature that normally could never be vanquished by just one pony. Upon hearing this, only two ponies, Snips and Snails, openly believe Trixie's claims and proclaim her as the the most magical, talented, and all around awesome pony ever. Rarity, Rainbow Dash, and Applejack, takes Trixie's challenge to see who is better, only to be humiliated one by one. Twilight, who feared that she might lose her friends if she showed off her magic like Trixie, doesn't accept the challenge and runs off, and Trixie proclaims herself victorious, ending her show.

When an Ursa Minor (that was mistaken as an Ursa Major) attacked Ponyville after being woken up from its sleep by Snips and Snails, Trixie used her magic tricks to try and defeat it, but they were useless. She then admitted that she can't defeat an Ursa Major and never had, having only made the whole thing up to make herself look better around others. Twilight then used her magic to soothe the Ursa Minor to sleep, gives it a "bottle" of milk, and sends it back to its cave in the forest.

Trixie was surprised to know that the monster they had faced was actually an Ursa Minor, the baby version of the Ursa Major, who went on a cranky rampage after being woken up by Snips and Snails. However, after the explanations, Trixie went back to her arrogance, saying that Twilight will never have the same power as her, and still claims herself about being 'Great and Powerful'. She then used a smokescreen to hide her exit from town. Rainbow Dash was about to go after Trixie, but Twilight stops her, certain that Trixie will someday learn her lesson about her bragging.

Trivia

 * A modified version of Trixie's cutie mark (purple wand and pixie dust and yellow star) can be obtained at the end of Adventures in Ponyville.