puts victims under a sleeping trance
The Trance Lance was the personal weapon of Sir Trancelot. With it, he could fire a trance ray which would instantly put a person under a sleeping trance when hit.
In the episodes My Present To The Future and Inside Out, Sir Trancelot fires a sleeping spell from his hand to put people to sleep, proving that he doesn't actually need to use his Trance lance for his signature move at all.
The Trance Lance was first used by Sir Trancelot in the episode I'll Be A Son of a Ghostbuster.