There are many many holes in this argument. First off the Gospels were written in the first 100 years AD, Mithraism began to spread after this. Even if you believe as do some that it was founded in the first century BC there is no evidence of its spread before the first century AD. Secondly, certain things are said as if fact, when they are simply incorrect: Mithraism held that all souls pre-existed in the ethereal regions with God, and inhabited a body upon birth. (This statement being used as a similarity between the two religions falls flat on it's face because, in fact, Christians do NOT believe the soul existed before the body. If they did abortion would not be so bad an alternative. Life is sacred and begins when God says it does... at creation of the human. Mithra had no mother, but was miraculously born of a rock, or the petra genetix (Well, now this is quite a bit different from saying he was born of a virgin, is it not?-- This from Wikipedia... I mean it just goes on and on. And as Justin Martyr points out the Old Testament, which certainly points to the new, did prophecy the virgin birth of the Saviour, etc... was well known across the western world at the time and by all religionists. Afterall, look how Islam liberally adopted and alternately corrupted the Gospels to suit mohammed's ultimately bloody fabrications. This is not new, this is old stuff.
Kalvin, yes, if by "Christ's" you simply mean the Messiah. But in the personification of Christ as Christ He Himself warns of a difference - and this is that many will come healing etc in His name, meaning attempting to suggest that they and HE are one in the same.
yes. They'll show many signs and wonders and if it were possible even the elect would be deceived. People can't even tell the difference between the Gods of the various religions. And that's easy.