Have you seen the ritual scene? You can get the pebbles from Mona’s bag, and the vial is sold by Mona as well. Also there’s a “hidden” scene with Marionette you can have before the succubus.
I haven't. I remembered the succubus told me I needed some items, but when I talked to her again she wouldn't mention them. Maybe that would be worth adding to her repeat dialogue? It's good for the player to always have reminders available of what their goals are.
