I'm going to be honest and say that I kind of already did make a custom spell, that being the Fearful Hex thing I mentioned earlier. It basically causes a target to experience unpleasant, vivid hallucinations for a while. 

In fact I really just intend to use custom spells as I honestly don't know many canon spells (save for a handful) and really don't feel like having to read through the entire list of spells until I find something I want.