The Servant of Lord Voldemort

Hermione screamed. Black leapt to his feet. Harry jumped as through he'd received a huge electric shock.

“I found this at the base of the Whomping Willow,” said Snape, throwing the Cloak aside, careful to keep his wand pointing directly at Lupin's chest.

“Very useful, Potter, I thank you…”

It was like watching a speeded-up film of a growing tree. A head was shooting upwards from the ground; limbs were sprouting; next moment, a man was standing where Scabbers had been, cringing and wringing his hands.