How truly powerful is an ailcorn?

Story summary: Starlight never accepted Twilight's offer of help. Many iterations of worlds and pasts have passed since. So Twilight gives up on mercy and tries something else. Something that she'll regret for the rest of her life.

Original story: https://www.fimfiction.net/story/418598/starless-sunlight

Music: https://www.youtube.com/user/myuuji