Ok, so plot wise you need to work on flushing out the reasons for things. Such as why they were there in the first place, your reason was very flat. They were there because twilight wanted to study it, and other than the city being an ancient pegasus city that might have traps dashs' reason is flat.

Next, i don't know if its just me but descriptions of the surroundings are always a good thing for setting mood for an area. As my english teacher always drilled into my head "show don't tell".

Lastly, your biggest error is one that many new writers get wrong is dialogue formatting. In dialogue every time the person speaking changes you switch to a new paragraph.

P.S. My first two points come with practice it takes time to be able to write those well. Other those your on your way to being a really great writer. Just keep writing and good work.

Dash is referred to as a he several times throughout.

https://www.deviantart.com/tiarastwilight/art/Devil-s-Divide-Seductive-Queen-Spectrum-Knight-TF-570158876

Which one of you is the real author?