In season four, episode twenty-one, "Darkest Plight", while battling Super Shredder in the under city, where he last faced the rat king, Splinter falls into a pit and sustains an injury to his leg. Here, he encounters the rat king, who encourages him to denounce his humanity. Eventually, he discovers the skeletal remains of his tormentor, and realizes the rat king was killed after their last battle, and that his appearance was nothing but a hallucination brought on by disorientation and fever. This is a direct callback to the Mirage Comic series "City at War", where similar events take place.