I know the 1 John 2:18 verse about antichrist has many confused. But that's not the only Scripture about the subject, and you don't have to see the word 'antichrist' actually written in other Scripture witnesses to know... that's what the subject is about. It's a matter of using simple common sense when studying.
The Greek word antichristos from Greek anti and Christos simply means one opposed, or in place of Christ. So would Satan fit that? Yes, of course. Also any man that opposes our Lord Jesus Christ, or says he's Christ is doing the same thing. Yet, just who did that first? Satan, of course, when he first rebelled against God, but how? By coveting God's Throne for himself, wanting to be God in place of God (Isaiah 14).
2 Cor 11:3-4
3 But I fear, lest by any means, as the serpent beguiled Eve through his subtilty, so your minds should be corrupted from the simplicity that is in Christ.
4 For if he that cometh preacheth another Jesus, whom we have not preached, or if ye receive another spirit, which ye have not received, or another gospel, which ye have not accepted, ye might well bear with him.
(KJV)
Paul feared brethren would be deceived by those that might come preaching "another Jesus". Important idea, because what is Paul revealing with that idea of "another Jesus"? Can there really be more than one True Jesus Christ? No, there cannot be, and that's the rub, because Satan wants... to be God, and worshipped as God. This is why it's so important to look up in the Hebrew what the word for "Lucifer" really is in the Isaiah 14:12 verse. The actual Hebrew word is 'morning star'. God is mocking Satan there, using Satan's own words against him, because Satan wants to be... The Morning Star, another Title for our Lord Jesus Christ per Rev.22. Do you see what Paul is revealing here then in 2 Cor.11?
Paul is speaking of two objects. One for the false ones that are preaching the coming of "another Jesus", and then the actual role of the "another Jesus". And farther down in 2 Cor.11, he makes it plain just who those false apostles are that come preaching that, and who the "another Jesus" is...
2 Cor 11:13-15
13 For such are false apostles, deceitful workers, transforming themselves into the apostles of Christ.
14 And no marvel; for Satan himself is transformed into an angel of light.
15 Therefore it is no great thing if his ministers also be transformed as the ministers of righteousness; whose end shall be according to their works.
(KJV)
Right there, you have both the singular "antichrist" idea that John said they had already heard shall come. And in the next verse is the "many antichrists" plural idea that John said are already here at work on earth.
This same dual object antichrist idea appears again by Paul in 2 Thess.2, for he was specific about a particular false one coming to sit in God's temple and exalting himself over all that is called God, or that is worshipped. And then further down, he mentioned how the "mystery of iniquity" was already at work. That "mystery of iniquity" idea is about the "many antichrists", i.e., the followers of the singular antichrist coming to sit in God's temple and work great signs and wonders to deceive the world with.
In Matthew 24, our Lord Jesus gave the SAME comparison, between Matt.24:4-5 and Matt.24:23-26. With the first, He said 'many' would come in His Name saying they are Christ. That's the "many antichrists" idea. But in Matt.24:23-26 He was speaking of a specific false Christ that's to come working great signs and wonders that would almost fool His elect if it were possible, and that's the idea of a singular antichrist. (The "false Christs" phrase in the KJV of Matt.24:24 is actually 'pseudo-Christos' per the Greek, and the 23rd and 26th verses are definitely about a singular false Christ).
So the antichrist prophecy is dual. It's about both a singular antichrist, which I will tell you right now, is Satan himself. And then his followers which work iniquity against Christ, even with many of them saying they are Christ already, those represent the "many antichrists". According to Scripture then, can't have "many antichrists" without a singular "antichrist"also.
And then lo and behold, what kind of false working are we told about that the "another beast" of Rev.13:11 forward is to do?
Rev 13:11-14
11 And I beheld another beast coming up out of the earth; and he had two horns like a lamb, and he spake as a dragon.
12 And he exerciseth all the power of the first beast before him, and causeth the earth and them which dwell therein to worship the first beast, whose deadly wound was healed.
13 And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men,
14 And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live.
(KJV)
To be compared with...
II Th 2:3-4
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;
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.
(KJV)
II Th 2:8-10
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,
10 And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.
(KJV)
And also compared with...
Matt 24:23-26
23 Then if any man shall say unto you, "Lo, here is Christ, or there"; believe it not.
24 For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.
25 Behold, I have told you before.
26 Wherefore if they shall say unto you, "Behold, he is in the desert"; go not forth: behold, "he is in the secret chambers"; believe it not.
(KJV)
That "another beast" entity coming to work miracles and great signs on the earth has been revealed to us by our Lord Jesus all along. It's just that the "many antichrists" exist today to try and get you away from understanding about that particular false messiah coming to do miracles on earth, and set himself up as God.