I always find horror even more horrific in watercolors. There's something so beautiful about the softness of watercolor even with a starkly brutal subject that provides a cruel juxtaposition of medium and matter.
You use this perfectly; the stark, post-Apocalyptic feel of the backdrop, the bones, the sacrifice, the bondage. Harry's scrawny form and Snape's power are perfectly silhouetted.
I find this stunning and disturbing. I'm fairly certain it will haunt me. Fantastic work.