A.T. Robertson Commentary Mark 5:7

"and crying out with a loud voice, he saith, What have I to do with thee, Jesus, thou Son of the Most High God? I adjure thee by God, torment me not." — Mark 5:7 (ASV)

I adjure thee by God (ορκιζω σε τον θεον). The demoniac puts Jesus on oath (two accusatives) after the startled outcry just like the one in 1:24, which see. He calls Jesus here "son of the Most High God" (υιε του θεου του υψιστου) as in Lu 8:28 (cf. Genesis 14:18f.).

Torment me not (μη με βασανισηις). Prohibition with μη and the ingressive aorist subjunctive. The word means to test metals and then to test one by torture (cf. our "third degree"). Same word in all three Gospels.