I was thinking the firebringer trilogy
http://www.fantasticfiction.co.uk/p/meredith-ann-pierce/and yes Pierce Anthony is funny but i dont remember reading Night Mare , just his Xanth series will keep you busy for a while and is also his best known work
btw if you like Pierce Anthony it might be worth checking out Robert Asprin, especially his MYTH series
http://www.fantasticfiction.co.uk/a/robert-asprin/