Satan opposes anything to do with God and His Son (Rev. 12:17). He is also a great imitator. John demonstrates this in the book of Revelation by means of "antithetical parallelism." Note the contrast between "a lamb as though it had been slaughtered" of 5:6 and the mortal wound of the beast (13:3). The lamb denotes Jesus Christ as the one who, by the surrender of his life even to the point of death in an act of service, is worthy to receive power (5:12). The beast represents the power given by "the murderer from the beginning" to commit acts of violence (11:7), and causes himself to be worshiped because of his power (13:3). Many more examples where that one came from.
I believe the GB is deluded. According to Revelation (6:15-17; 7:1) the sealing of the 144,000 is a future event. "After this" means what came before. When the kings and their following flee to their underground shelters, only then will the sealing take place. God will decide who is to be sealed.