The Lake Knights make their only appearance in "My Two Favorite People." When Jake tries to spend more time with both Finn and Lady Rainicorn at the same time, he realizes that this can only be done if he fetches the Universal Translator that he threw into the lake. The Lake Knights guard the lake, translator, and a massive pile of doubloons and treasure (which remained untouched by the trio) with swords. After fighting off a horde of Lake Knights, the three get the translator and safely leave. According to Finn, they are evil.
They have dark aqua skin and a light blue stomach. They also have a silver cone on their head, circular maws and asterisk-like markings instead of eyes (they are probably eyeless or blind). They wield a bright yellow sword with a blue hilt.