I might find an answer to your question - even tho I can no longer find the question!
It seems to me that a while back (I have no concept of time) you had a question (you were relaying from someone else) about Christianity's main teachings (Death of Christ, Resurrection, Rebirth of Believers, etc) originating in ancient Pagan Myths.
Well, I finally found a great reference for you - tho I'm not sure you need it any more!
Josh McDowell's book,
A Ready Defense has a chapter (14. P162 in my edition) "Is the New Testament Filled with Myths?" It gives a nice, thorough discussion in case the topic still interests you or your friend. and it's not excessively long or complicated to read. Well footnoted, tho, if you need more info.
I highly recommend this reference for every home anyway (not that I don't disagree with it ever ; ) It's a great resource : )
And you can get it used really cheap! https://www.amazon.com/Ready-Defense-Best-Josh-Mcdowell/dp/0840744196/ref=sr_1_sc_1?ie=UTF8&qid=1517801257&sr=8-1-spell&keywords=josh+mc+dowell+a+ready+defense