'Brilliant' doesn't even begin to describe this! It's funny and perfect and amazingly drawn, and the details are really stunning. I love Snape's red face and hairy legs--actually, I just love the way you've drawn him, full stop. Ditto for Filch, who looks age-appropriate, with his receding hairline and saggy belly. I just can't get over all the textures and small details, though--the pictures, the lube, the manacles on the wall.
I was so hoping to see this pairing represented here, and this is a great example of it!