This circular reasoning again, here's what the bible says (again):
He can appear as an angel of light. 2 Cor 11:14 (see also D&C 128:20, 129:8)
He will seem to be like God. 2 Thess 2:4
He will not be exposed as the devil until the end of time. 2 Thess 2:8
His followers will seem (and claim) to be apostles of Christ. 2 Cor 11:13-14, Matt 24:4-5, 24:23-26, Mark 13:21-22
His followers will be able to do miracles and wonders. Matt 24:24, Mark 13:22
He will tempt with the promise of dominion and power. Matt 4:8-9, Luke 4:5-7
He will be able to deceive even the "elect" (i.e., the righteous and the saved). Matt 24:24, Mark 13:22
He (and his followers?) believe that they will be like God. Isaiah 14:13-14
The devil's followers are whoever sins (the righteous - the followers of God - do not sin). 1 John 3:6-9
Feelings are the imaginations of the heart (and are deceptive; thus they may come from Satan) Jer 17:9 (also 3:17, 7:24, 9:14, 11:8, 16:12)
Every man thinks that he is right (implicitly, this includes even those who are deceived; thus, even though you may think you are right, you may still be deceived). Prov 21:2
Those who think they are standing (i.e. correct) will fall. 1 Cor 10:12
The devil's false prophets lie; true prophets of God do not. Deut 13:1-3, 18:20-22, Isa 9:15, Jer 5:31, 14:14, 1 John 2:21, many other passages
But sometimes the devil will tell a truth (Mark 1:24, Luke 4:33-34, 41, Gen 2:4-5)
Joseph Smith also taught that sometimes false angels and false revelations from Satan are difficult to recognize as false. He gave as one test the hair color of an angel - if it is sandy-colored, the angel is not from God (Teachings of the Prophet Joseph Smith, p. 214). Another test is comparing the message of the supposed angel to previous revelations: if it contradicts previous revelation, it is from Satan (ibid.).
3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;Which says pretty clearly that there will be a falling away from the truth... And that this falling away will reveal the "Man of Sin". Later, in : 2 Thessalonians 2:8
4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.I hope everyone can clearly see that there will be a falling away. this falling away will eventually be revealed as the work of the antichrist in the last day (so it's not that Satan will only be revealed in the last day, that's a misinterpretation of the scriptures from taking them out of context.)
5 Remember ye not, that, when I was yet with you, I told you these things?
6 And now ye know what withholdeth that he might e brevealed in his time.
7 For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way.
8 And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming:
9 Even him, whose coming is after the working of Satan with all power and signs and lying wonders,