Well, before they try summoning one, they should know that it will not my physical, they may not be able to see it, hear it, or even feel it. They must be well trained enough to even be able to KOW that they have sommoned something. Tell them to do more research before even attempting this. Tell them to practice spirit communication, it is a good place to start.
I am new to this site. But not new to the strange, and un-explainable. I have been encountering these ??? what ever they are. for the past couple of years. I haven't told anyone, fearing that they would think that I had lost my mind. If I didn't know myself very well. I would of thought I was hallucinating. But I keep experiencing these encounters.I never see them. But I smell their perfume, I hear them talk, I feel them touch me. They don't scare me. But I have heard that they will eventually kill you. is this true ??? thanks... firstname.lastname@example.org
Its very dangerous to summon one. As ElementalGuy said, if your friend is male and he summons a Succubis he will die a very painful death.
Even if your friend is female, its dangerous, and she may even be possessed by the demon.
Its not a very good idea.