Im looking for stories where discord is just absolutely terrifying, as the title says. any good recommendations?

A dash of humanity.

Terror hmm? It’s been a long time but these popped into my mind. Have fun staring into the abyss!

Providing the Rope (more DARK AF then scary)
Rot
I have no voice and I must Cry
And of course: Thus dwell in joy

I don’t know how well these will fit your criteria but...

7480880
Lunaverse Discord has yet to appear but whenever his presence is felt its really scary.

"Getting serious". It's pretty cruel