The fast-food chain Fat Shack, which gained a boost after its co-founders recently appeared on Shark Tank and received a six-figure deal, has opened a location called Fat Shack Underground in Pioneer Square. The business specializes in hedonistic menu items like "fat sandwiches" stuffed with various combinations of mozzarella sticks, chicken fingers, French fries, onion rings, jalapeño poppers, and mac and cheese, as well as buffalo wings, burgers, Philly cheesesteaks, and deep-fried desserts made with Oreos, Rice Krispy Treats, Twinkies, chocolate chip cookies, and funnel cake bites.