The Electrode Gun is one of Princess Bubblegum's science inventions seen in the episode "Lady & Peebles." Princess Bubblegum introduced it to Lady Rainicorn to prove her not to worried about them getting into any trouble.
It is a gun-like weapon that has a purple ball of electricity with a pink center on the end of the weapon. The ball is full of electricity, hence the name "Electrode Gun". Inside is lightning like.