The Lantern first appears in the episode "Incendium." It was used as a containment device to protect Flame Princess from burning through the Earth. According to Princess Bubblegum, she had Flame King lock Flame Princess in the lantern in order to prevent her from melting through the planet and burning it if she were to experience extreme romance due to her elemental matrix instability. In "Earth & Water," Flame Princess discovers that she is stronger than Flame King and overthrows him by trapping him in the lantern he once trapped her inside of. In "The Red Throne," after Flame Lord was defeated and knocked out by Flame Princess, she throws him into the lantern and locked him with Flame King.
It is a giant lantern capable of holding Fire Elementals. The glass is a dark yellow with the base of the lantern being yellow with orange triangles. The base of the lantern has three knobs (one behind the lantern to the viewers) that are connected to ropes that suspend the lantern.