Who tries to stupefy Harry Potter in the department of mysteries?

In the Department of Mysteries, Harry Potter is not stupefied. He is attacked by Bellatrix Lestrange, who tries to kill him.

It's important to remember that stupefy is a spell that disarms and renders a person unconscious. While there's a lot of fighting in the Department of Mysteries, Bellatrix's intent is to kill Harry, not simply to incapacitate him.