Ah, yes, you’re right. I meant more “empty of shapes in $medium”, but there was maybe some chalk drawing in the square unless they were careful to use a rare means of creating the circle.
Two summoning circles, one for a demon, one for an angel, in a larger boundary. Binding to restrict them and their effects to the larger space. Audience. No task.
(b) I am totally stealing that and backstorying that at some point someone tried that and ended up getting Lucifer (Jean) and his sister, resulting in a very confused audience as they hugged and burst into tears
This can work even if the “larger boundary” concept cannot. You just need to project the circles in turns, or draw them on a horizontal computer monitor, or something.