The Electrode gun is a weapon that Princess Bubblegum created in order to rescue Finn and Jake in "Lady & Peebles." Princess Bubblegum did not use it, but she did use her other invention, the Ball Blam Burglerber. It was also snatched while she was searching for Finn and Jake.
The Electrode gun appears to be similar to a plasma globe with a gun grip along with a trigger. The body of the gun is purple and it emits a magenta colored lightning.