User blog comment:FairyRaven/Fairy Tail Chapter 388: Erza vs. Minerva, Review and Commentary/@comment-7418318-20140613082335

I'm afraid.

Mard was shown to be vulnerable to light and Sting uses something like light magic (not exactly, but close enough).

Please Mashima! Don't let Sting beat Mard Geer all by himself! That would suck sooooo much.