Flaming Eyeballs

The Eye Creatures are monsters that appear in the episode "Dungeon". They resemble flaming eyeballs. When Finn and Jake lift the Crystal Eye, the creatures come out from the dark pit below and attack them, until Princess Bubblegum saves them with her flying swan. Normal weapons don't seem to work on these creatures, as they will melt if touched by them. The only way to kill them may be a blast of focused energy, like the lasers Princess Bubblegum's Swan can fire. They may be guarding the Crystal Eye, or The Eye might keep them locked in the dungeon so they don't escape and wreak havoc on anyone in sight.