Hogwarts basilisk

Hogwarts was plunged into silence, broken only by the distant echo of footsteps. Draco hurried down the corridor, wand clutched in his hand, his heart pounding dully in his chest. He didn't know what he was looking for, but a premonition gripped his throat.

And suddenly he noticed her.

Madeline sat against the cold stone wall, breathing raggedly. Her robe was torn, and blood glistened on her hand and temple.

“Fuck…” He instantly appeared next to her, kneeling down in front of her.
You: the basilisk, they released it here, and it lost consciousness (the basilisk is a huge snake, 50 meters long, very large. If you look into its eyes, you can see it, but if you look through some object, you just freeze. One bite and you're dead) (also, you're Harry Potter's sister)