One spell I have never used, but which I liked from the start, is Gestalt, from BOEMII.
I needed to look that one up. (I found an informative review at AtFantasy.) For anyone else who doesn't have the Book of Eldritch Might II (from Monte Cook), Gestalt merges two creatures into one.
It sounds like Monte's book presents a few "flavorful" spells: Feedback, which deals damage if a specified action is taken; Legacy, an illusion that stores a programmed image of you triggered by a certain circumstance; and Animate Necrosis, which makes a target’s wound attack it.