While the Greek texts can typically be translated as ‘antichrist,’ the Aramaic text makes it abundantly clear that it says and means ‘false anointed one,’ or ‘false Christian.’
‘Christ,’ of course, just means ‘Anointed One.’ Every Christian is an Anointed One (‘Christian’ literally means ‘little anointed’), and Jesus is also called the Anointed One.
The ‘Anti-’ part in Greek could mean ‘opponent’ or ‘opposite’ but it can also mean ‘like’ or ‘reminiscent of,’ which basically means fake. The Aramaic clarifies what was meant, since the Aramaic word clearly means ‘false’ or ‘liar’ – again, fake.
So when most Bible says ‘Antichrist,’ this is a mistranslation. The word actually means a fake anointed one, or a fake Christian. Note that it may not refer to a false ‘Messiah’ because the context in 1 John 2 describes some of these ones – they are ordinary Christians who now ‘deny the Son.’
How could anyone falsely identify as an anointed one (a Christian), and deny the Son? Well, remember that the gnostic ideas were the first real heresy in Christianity – and one gnostic teaching was that Jesus was merely an ordinary human who attained ‘enlightenment’ through studying wisdom (known as ‘gnosis’).
So the fake anointed ones mentioned in John 2 may have been Christians who had been seduced by some gnostic teaching that ‘denied’ Jesus in some manner.