Thorny

Attacks by rolling in a ball towards the player, dealing contact damage and knock-back. Dodge roll through their roll attack and attack them when they get out of their ball form.

If you attack these enemies while their spiked back is facing you, you will inflict damage upon yourself

Design
In the early days, Thorny didn't have any spikes on his back. Instead, he only had the sort of shield and was named "goat" in the game files. His attack was the same as thorny according to the spritesheet.

Along with the fact that Thorny is called "satyrSpike" in the game files, this suggests that his design was inspired by the mythological Satyrs. Indeed, Satyrs were often represented as part goat with horns on their forehead, much like Thorny.