"Alohomora!" Remus incanted, sending a jet of light at the wardrobe. The door burst open, and out came a gaunt-looking woman with thick, shining dark hair and heavily hooded eyes. She looked familiar, like Harry had seen her before.
In the quiet, Harry just about heard Remus quietly say "Oh, bugger".
"YOU!" Neville bellowed, then turned and darted for his bag.
Startled enough he wasn't sure how to react, Harry watched as Neville reached into his bag, pulled out an iron bar about two feet long, and swung it at the woman like a cricket bat.
"Riddikulus!" Remus snapped, and when the bar connected there was a loud BONG sound. Little birds circled the woman's head, and she wobbled around a bit before falling straight over backwards.
"Blimey, Neville, what was that?!" Dean demanded.
"That's – Bellatrix Lestrange!" Neville replied, panting. "I… wait..."
He blinked, stepping back. "No, it's a Boggart, isn't it?"
"That was a hell of a reaction," Seamus said.
The Boggart cracked, changing shape, and a bloodstained, bandaged mummy was walking slowly towards Parvati.