BEHOLD!!!

Earth Pony

Unicorn

All joking aside, let's discuss this. Which do you prefer? To write her as an Earth pony or a Unicorn?

Unicorn.

Unicorn. Her mane's covering her horn.

I prefer Unicorn Raven... Plus, as the others have pointed out, that's due to her horn being obscured.

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Her horn is just small enough to be easily covered by her hair... Now I want someone to draw this but with MLP characters instead of FO:E characters and have Raven in the place of Blackjack

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6470741 It should be noted that the wiki, says has appeared as both... which is admittedly odd.

It is possible that there could be a spell or potion that allows an Earth Pony to temporarily gain a horn, kind of like that one time, Rarity gained wings (before losing them in her vanity and plummeting).

I mentioned this in another thread, but I think it was intended for her to be a unicorn all along, BUT you know how the animators miss some details here and there.
*cough cough* alicorn guards *couch cough*

But my head-canon is that with her being both, who's to say that she was an Earth-Pony that earned her magic when she went from working in Ponyville--as her appearances have her with Mayor Mare--to working for Celestia in Canterlot.

Or she has a secret twin-sister who is an Earth Pony, known as 'Writing Desk' to the fan-art community, as her name is actually not spoken in-show.
But more likely, just an animation-error brought on by her only being seen in four episodes.