Some "Green Man" info - from one of the few places that did not list Cernunnos in the same breath:
GREEN MAN (The Hidden One - The Cylenchar) The next stage of the ecological revolution begins with the reawakening of the male counterpart of the Goddess, the Green Man, an archetype found in folklore and religious art from the earliest times, and especially linked with the Christian origins of modern science. Long suppressed, the archetype emerges now to challenge us to heal our relationship with nature. - It is likely that Green Man pillars were erected originally on the sites of sacred trees. The Green Man signifies irrepressible life. He is an image from the depths of prehistory: he appears and seems to die and then comes again after long forgettings at many periods in the past two thousand years. In his origins he is much elder than our Christian era. In all his appearances he is an image of renewal and rebirth. See also: JACK IN THE GREEN.
JACK IN THE GREEN (The Hidden One - The Cylenchar) The Woodland spirit who, like the Wood-Wose or Wild Herdsman, guards the greenwood. He appears in many kinds of folk art, as a multi-foliate head peering through the keaves. Like the Sheela na Gig, he was especially portrayed in church decoration, usually as a roof-boss, where he was a constant reminder of earlier beliefs.
Interestingly, the same site I got that info from mentions Aoife being "turned into a witch of the air" - wonder if that could mean she could train Josh in Air magic? Assuming she is open to help given that she cam looking for what happened to her sister?!