The taser is a weapon used by the Gnomes in the Beneathaverse in the episode "Power Animal." It is a long pole with an electrical shocker at one end. The Gnomes tase Finn to make him run faster on the Cyclonic Rodentarod.
Gunter uses a miniature version of the taser in the episode "Princess Potluck," which, just like its larger counterpart, can produce a bright electrical shock capable of hurting someone slightly. Gunter uses it for self defense against Ice King and Finn, who tries to take a sock from his/her dress.
The large taser has five blue disc-shaped objects connected to a long rod, one of the objects is at the tip of the rod and produces the electricity.
The mini-taser has a black handle with a red button on it, and connecting to the handle are two balls capable of producing electricity.