Transmogrifian Torture
From Harry Potter Wiki
The Transmogrifian Torture was a curse which Gilderoy Lockhart suggested could have killed Mrs. Norris (before it was discovered that the cat had only been Petrified). Lockhart claimed to have witnessed the spell more than once and stated that he knew its counter-curse.
Since Lockhart based his entire career on lies, it is unknown if the Transmogrifian Torture is a real spell, or simply something which Lockhart made up to make himself look like an expert in the Dark Arts.
