Black Turtles

The black turtles are animals that appear numerous times throughout Over the Garden Wall.

Physical Description
Black turtles are very small turtles found in forested areas in the Unknown. Their skin is a desaturated green, their carapaces are black, with four bumps arranged in a symmetrical diamond pattern, and their plastrons are slightly lighter than their skin, with four or five parallel lines spanning them horizontally. They have circular black eyes, no visible mouth, rounded head and legs, and a short, pointed tail.

Role in Over the Garden Wall
During Wirt's and Beatrice's conversation in The Old Grist Mill, Greg sees a black turtle and sticks a piece of candy to its shell. Later, it is revealed that swallowing that turtle was what turned Beatrice's dog into the monster that attacked the boys and destroyed the mill.

In The Ringing of the Bell, Auntie Whispers is shown to keep a large basket full of black turtles, which she eats. When Lorna arrives at the house, Greg exclaims that he came to "burgle [her] turts," and when she warns Wirt and Greg to hide from Auntie Whispers, they hide in the basket of turtles.

Appearances

 * The Old Grist Mill: See Role in Over the Garden Wall.
 * Schooltown Follies: When the brothers stop at the school, one crawls over the overturned tree before the racoon picks it up and throws it into the water.
 * Songs of the Dark Lantern: At the very beginning the Woodsman is seen looking at one crawling on the ground, before he's distracted.
 * The Ringing of the Bell: See Role in Over the Garden Wall.
 * Babes in the Woods: During the beginning of the Cloud City sequence, an anthropomorphized black turtle can be seen walking alongside Greg in the bedcart.
 * Into the Unknown (chapter): In Wirt's bedroom, there's a band poster with one, the poster also reads "Black Turtles".
 * The Unknown: The epilogue shows the Fisher Fish catching one.

Trivia

 * Despite their relatively frequent appearances (they appear in more episodes than the series' primary antagonist), the black turtles serve little to no purpose in the story.