Lady Rastan rolls her eyes. "A single meaningless gesture," she hisses. "Do you think that those in the corridors of power would have permitted Cavalcade Academy if they thought that it would work?" She waves a hand, dismissing your argument. "The school was always meant to fail, and that failure would allow humanity to continue to ignore and marginalize the undead. Well, no more."
She throws out an arm, and you're thrown back by an unseen force, tumbling painfully over the rock plateau. Rastan raises her hands into the air, throwing her head back. "Arise, Renzfal!" she exalts, her voice filled with an insane fervor. "Rise from your prison and take your rightful place astride the world! Come, Renzfal: your servant has liberated you!"
A terrible rumbling roar answers, shaking the mountain peaks and the plateau you're standing on. Your heart leaps up into your mouth, your body freezing as sheer terror takes you over.
And then it happens.
A head, monstrously, grotesquely huge, rises, looming above the plateau. The size of it is unfathomable. A single one of its three burning red eyes is larger than the whole of Cavalcade Academy. Below them, stretching out so wide that they could swallow St. Mary's in a single gulp, two mouths lined with jagged black teeth hang open, displaying a white serpentine tongue. Its bloody, scarred skin seems to writhe over its flesh, and for a single mad moment, you'd swear that you could make out countless shrieking faces in the meat.
Renzfal is free. Renzfal has come.
Lady Rastan lets out a wild, breathless shout of laughter. "And now for the final spell, my dark prince!" she exclaims. "With this, you shall pass into this vessel!" She indicates your aunt's slumped form, and Renzfal's three colossal eyes fix upon it.
"AT LAST!!" Renzfal's voice is like the thunder and the cracking of stones, the undertone a guttural growl. "WITH THIS SACRIFICE, I SHALL STRIDE ACROSS THE EARTH ONCE MORE, EVERY FOOTFALL BRINGING DEATH!! THE WORLD SHALL FALL, AND EVERY LAST SOUL WILL SCREAM MY NAME!!"
Lady Rastan's voice sounds again, chanting rapidly in a harsh incantation. These could be the final spells needed to free the monstrous demon.
Possibilities, plans, and their consequences sprint through your mind, each one passing by in a single shared instant. You could try to destroy Renzfal's chosen vessel—Aunt Cavalcade—though if Lady Rastan catches you, then you're as good as dead.
Of course, Lady Rastan's presence might work against her own plan as well: magic of this power requires incredible focus, and a distraction at the right time could foil her attempt to release Renzfal. It could even be calamitous enough to finish the pair of them. Or, if either the vice principal or the demon could be tricked into turning on one another, it might even be possible to trick them into dooming themselves.
Beyond that, you're left with Matron's device or the prospect of thwarting Lady Rastan through magical means. You'd either need true faith in your own eldritch knowledge or the nerve to pin your last hope on Matron's scientific brilliance.
Whatever you're going to do, you need to do it now.