I agree it would seem that Satan's modern visage would be a direct reaction to the Cernunnos/Pan cults the early Christians would have had conflict with. In the same vein, the local deities of the Celts (and others) that could not be burned from the consciousnesses by the usurping faith were cannonised as saints and outfitted with bogus stories that melded their original qualities with sometimes absurdly false connections to Christ or miracles performed in His name.

Satan and Lucifer are often thought of as the same thing, particularly in the Evangelical world, but there is no real connection within the Bible. Lucifer seems to actually reference a terrestrial Babylonian king. Satan is a title meaning "one opposed to" or "adversary."

Satan in the OT is referenced many times as both an adversary of the simple human sort, and as God's right-hand man when it comes time to doing some evil deed. He is sanctioned by God, and is not His adversary, but man's. In Rev., Satan gets a makeover from the wildly creative author and takes on his modern role as God's adversary, though this Satan may not even be the same being as that referenced in the OT or even elsewhere in the NT.

Back to image, I think that the classic depictions of a grotesque creature with blended attributes are the best images of Satan. Goat's head, single cloven hoof, Hermaphroditic body, & etc. Little forehead horns and pitchfork, seriously? Though the depiction of Darkness in "Legend" is really good as well, but I wonder what he was making up for with horns THAT size.