Sludge is a monster living in the sewers in the Fast Forward-based comic No Place Like Home. It returns in Peace Keepers as a member of the Triumvirate of Terror.
The Turtles first encounter Sludge when investigating the contamination of the city's water system. City workers previously sent down to find the problem never returned, so Splinter tells the Turtles that they should learn what is happening. They aren't in the sewers long before they are attacked by Sludge, who tells them its name and that the tunnels belong to it. Sludge lashes out at them with its many tentacles, but they beat a hasty, strategic retreat. Sludge pursues them, but Donatello collapses a crumbling stone brace on it. While Sludge is momentarily immobilized, the Turtles look for a way out, but enter a spillway with water pouring in from all sides. With Sludge free and once again after them, the Turtles use some boards to surf their way out of the tunnels. Sludge is swept along behind them and lands in a wire net, after which it is taken into custody by Aloysius Biggles.