Angle Moroni was known as the "Angle of Light" This was written in the Doctrine of the Covenants introduction until it was changed in the 1950's (go figure) Elder Bruce R. McConkie (McConkie was a member of the First Council of the Seventy of the LDS Church from 1946 until his calling to the Quorum of the Twelve Apostles.) McConkie authored the widely read Mormon reference work titled Mormon Doctrine. In that book, McConkie equates the term “Angel of Light” to no other than Satan himself!
Galatians 1:8 if we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
Fictional characters can be anything we wish them to be. We can decide, for instance, that Luke Skywalker joined the dark side as a toddler and is fooling everyone. Or that Harry P. is actually the soul of Voldemort in disguise.