Jacqueline takes the appearance of a lantern with with nine small holes, in rows of three, on each side. Also, there is a circular handle with a chain attached. There is a handle at the end of the chain. When opened, the inside of the lantern takes the appearance of an angry Jack-O-Lantern.
Jacqueline, along with weapons like Soul Eater, has the ability to partially transform into a weapon. In Jackie's case, she can turn her hand into a lantern to spew fire like a flamethrower. Also, as seen in Soul Eater NOT!, she can turn into full weapon form and can fly without her Meister.