Writing Prose quality check?

[MFontana]

I want my prose to be light mostly? But also heavy in description when there is a need(which I started implementing in a way in my recent chapters as the chapters prior to this one are just too vague). Because I think for my dark fantasy novel this way is the best.

Then you'll definitely want to read and study C.S. Lewis' style as a reference point.
In particular, his Narnia series.
He tended to favor a lighter style that was full of layered description, and could be a solid go-to stylistically speaking.

The best advice I can offer is that description follows action.
In short, don't just describe what is there. Describe what it is doing, and layer the details in with the action.

As a quick example:
DON'T

The man had blond hair. His eyes were blue. He stood in the doorway and looked around the room.

DO

The man's blond hair swayed in the sudden breeze as he opened the door. His icy blue eyes scanned the room before him as his bangs once more settled to frame his face.

Beyond that, creating a sensory experience for the reader relies on utilizing more than just sight.
What does the character hear? Feel? Think? Taste? Smell? (As appropriate to the moment, of course).

Metaphor, Simile, and other poetic literary devices are fine for use even in Dark Fantasy, and are often employed to set or enhance the mood or tone in any given scene. If you're aiming for that classical gothic tone, I would strongly advise referencing the authors who really popularized it. Mary Shelley and Anne Rice. Though their styles are far denser and weightier compared to Lewis' or even what you might be aiming for, they would still be solid reference points for any delving into the use of poetic metaphor in Dark Fantasy.