Hailing from a part of the world that he refers to only as Below, Subterranean Cat is an NPC who appears during holiday events. Like most cats, he loves shiny objects, especially since they reflect the little light that can be found in his underground home. Although sneaky and mysterious, he seems to be mostly helpful, and he's always happy to give anyone a hand (or paw) as long as they'll bring him sparkly things in return.
He made his first appearance during the 2014 Frilly Heart Day event. In this event, he traded baking ingredients for Shiny Fish Trinkets, at a ratio of one ingredient to five fish.
Later in the month, he set up his own event, and traded rare eggs for crystal hearts that could be found by clicking growing eggs and foals. After a bit of convincing, he began taking bribes of silver in exchange for these crystal hearts, with the promise that the hearts would be traded back to him later.
He has also made appearances during the annual anniversary events, during which he utilizes his supernatural ability to open portals to other parts of the world. As usual, he has his own goals in mind during these events, as he asks players to send their horses through the portals in search of Shining Gold Gems. In addition to allowing players to keep anything else their horses find, he also allows them to pick special black and white anniversary horses from his Squirming Bag in exchange for the gems and gold coins.