The golden sword

The golden sword (also known as Scarlet) is Finn's weapon of choice throughout most of seasons one and two. The blade is dented, chipped, and dirty. Its hilt is black with some worn leather grip-straps and a red gemstone in the pommel. In "Business Time," the Business Men polish and sharpen the sword, making this episode the only one in which the golden sword appears to be in excellent condition.
In "The Real You," the golden sword passes through the Bubble creator and becomes four-dimensional. When Finn uses the 4-D golden sword to attack the black hole he created, Finn's golden sword is sent into the Cotton Candy Forest by the explosion. Finn is without a sword until "Mystery Train," which could mean he lost it after the explosion.