The Crystal Guardian appears in “Tree Trunks”. It’s not to be mistaken for the Crystal Guardians, who appear in a different episode. When Finn, Jake and Tree Trunks reach the crystal gem apple, the crystal guardian jumps out and mimics Finn and Jake, and when Finn punches it, it punches back, just harder. Tree Trunks begins to dance and the crystal guardian mimics her instead. Finn and Jake asked the guardian “Tree Trunks style” by putting on makeup and asking politely if Tree Trunks could go and take the Crystal Gem Apple. Its known forms taken have been Finn, Jake, Tree Trunks, and some butterflies.