The Gauntlet of the Hero

The Magic Gauntlet is a mystical weapon that is able to harm and slay The Lich. Princess Bubblegum gives it to Finn in the episode "Mortal Folly." The Gauntlet was destroyed during Finn's battle with The Lich.

Appearance
The Gauntlet is silvery-blue with five fingers and a thumb. There are metal bands on every knuckle and the wrist. A blue gemstone is attached to its forearm. On the top of the hand is an eye which can open and close on its own.

Trivia

 * The gauntlet was seen to be used by Billy during all of his adventures in the past. He has been shown to not possess it by the time Finn meets him in "His Hero." (Though it could be due to being hidden in another secret passage of Princess Bubblegum's castle, shown in "Mortal Folly.")
 * The eye on the top of it could represent the all seeing eye, which is said in ancient culture to see everything.
 * Like Billy himself, the gauntlet has six fingers as opposed to the typical three fingers nearly every other human and humanoid in Ooo possesses.
 * While Finn and Jake are chasing the Lich over the lake in "Mortal Folly," the gauntlet is briefly seen with seven fingers.
 * The gauntlet seems to possess some degree of life and sentience, as it shed a tear when Finn hit it in the eye to make it stop firing a magical blast and wouldn't work for him again until he apologized.
 * Strangely, Billy wears the Gauntlet on his left hand, while Finn wears it on his right. It is possible that two Gauntlets were forged and at one point at least intended to be worn as a pair or that it can change its form to fit the wearer.
 * According to Adam Muto, Billy may have entrusted his gauntlet to Princess Bubblegum before his retirement.
 * In the episode "Rainy Day Daydream" when Finn and Jake go to the armory in the tree fort, there is a cosmic gauntlet that looks similar to Billy's, except it is golden.
 * Jake calls it "Billys old beef fingers" which may be a nickname to this weapon.