The first question is whether musterion should be interpreted as being in apposition with onoma ? If not, John would be saying that the name on the womans forehead is Mystery Babylon the Great. If so, John would be saying that the name Babylon the Great written upon the womans forehead is a mystery. . . . The repetition of the womans title as Babylon the Great (Rev. Rev. 14:8+; Rev. 16:19+; Rev. 18:2+) rather than Mystery Babylon the Great favors the appositional relationship.1
By printing (on its own authority) the word mystery in large capital letters, the AV. has made it appear as part of the name. The Revisers have followed this example, printing the name in small capitals instead of large. But they have, in the margin, said or, a mystery, BABYLON THE GREAT, as though the word mystery did not form part of the title. We believe this to be the case.2We also observe that in the immediate context, the angel offers to tell John the mystery of the woman and of the beast which carries her (Rev. Rev. 17:7+). This provides further evidence against taking mystery as her title for the mystery pertains to understanding the vision, not her character. Moreover, the mystery extends beyond the woman herself to include the seven-headed beast with ten horns. In fact, an examination of the remainder of the chapter will show that the angel spends more time discussing the mystery of the heads and horns (Rev. Rev. 17:8-14+) than the woman (Rev. Rev. 17:15-18+). Although the Beast predominates in the explanation of the mystery, he has no such title. Thus, we disagree with the terminology Mystery Babylon, which is often used to define a second Babylon of sorts which bears little, if any, relationship to the city. This we believe is a misreading of the text and an unfortunate side-effect of how several translations have chosen to render Revelation Rev. 17:5+.
1 Andy Woods, What is the Identity of Babylon In Revelation 17-18?.