An incinerator is a rectangular pit in the ground which contains what appears to be magma or molten metal.
It is usually used to kill objects by melting or burning them. In the first season, it is also known as the metal furnace. So far, it has only been used on contestants and recovery centers.
In "Zeeky Boogy Doog", Golf Ball has one in her underground factory. Golf Ball uses it to kill Fries after being insulted by him. When Gelatin uses freeze juice on Golf Ball, his plan backfires when the incinerator activates a net to prevent her from falling in and deactivates when Gelatin is left on the incinerator. Tennis Ball uses it to kill Pencil and Coiny uses it to kill Bomby and indirectly all the contestants in the factory.