So while working on my story I went back and started rewatching the series up to the alicorn amulet episode. While later episodes do have Twilight casting offensive magic (like freaking laser beams). Most of her early casting attempts have her consulting books for magic. Actually now as I type this up until she gets her wings...she doesn't really just cast much outside levitation.

Then again, the alicorn amulet episode has her in a wizard's duel against Trixie. So obviously she must know some magic by heart. But if she were cut off from her books, just what kind of power would she have?

Twilight is book smart. If it doesn't exist in some sort of record form, she won't be able to implement it. Aside from her handling of the ursa minor in boast busters, I don't think I've ever really seen her exhibit any sort of 'out of the box' thinking. I don't count her coming upon the solutions to problems in friendship is magic, magical mystery cure or discovering her key to the box of harmony in Twilight's kingdom because that was more because of the spark of her element than her own cognition. Her battle with Tirek was not much more than knee jerk reactions and pumping as much raw power into apparently ineffective attacks as she could. As for her duel against trixie, that was all stage magic, not real spells.

But if she were cut off from her books

She'd have the power of the world's most extreme freakout.

'Extreme freakout' - remember Lesson Zero, where she cast the want-it/need-it spell with no books.

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In "Winter Wrap Up" she cast animation spell on snow plow without any book.
In "Boast Buster" Spike said that Twilight know "twenty-five different types of tricks". IIRC it includes "mustashe spell", "summon door" spell and "mouthszipper" spell. All of them she cast without books.
In "A Canterlot Wedding" she shoots changelings with some sort of concussion blast spell.
In "Crystal Empire" she reverses gravity. Again IIRC without boos help.
Teleportation, obviously.
Well, it's what I remember right now and her actual repertoire of spells could be bigger than that.

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Hmm, good points. Though the animation spell could have been looked up since she likes to prepare (or rather over prepare) for things. I'm just trying to nail down some consistent spells for her to have at the beginning of the story I am writing, and unfortunately for someone who is always consulting books for her magic...it makes it hard to gauge what powers she should be able to have on her own.

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Oh freakouts are going to be aplenty in my story. Both from her and the OC that are going to have to learn to tolerate each other. >:)

You can't exactly hold it against Twilight during the Tirek fight. She was clearly overloaded by magic. When fighting NMM she displayed guile by baiting her into attacking, only to teleport out of there. Against Starlight she copied most of her spells to use against her. Yeah, it was mostly lasers, but lasers have shown a variety if effects. So maybe they were "haxy" spells, except they either missed or got blocked. Against paprisites she cast a spell to alter their metabolism. She tried a anomaly reversal spell against Discords magic, and so much more.

Come to think of it Twilight actually does use spells to solve her problems. Like, all the time. It's just she gets PIS treatment so we can have a "crisis".