The Thing With No Name is a creature that lives in the Lake of Doom inside a cave in a mountain on the south end of the forest, which appears in the cartoon show episode "A Mere Truffle". It appears mostly as a series of tentacles that emerge from the water. It mostly goes after truffles, which the Truffle Trolls bring to satisfy its appetite, though it may also go after other things.
In the story, the group of Smurfs led by Tracker who were caught stealing truffles in the area where the Truffle Trolls normally go to look for truffles were placed on the island in the middle of the Lake of Doom for the creature to have its way with them. Later on, Papa Smurf's group of Smurfs who made it inside the trolls' cave saw what the creature was after and had Jokey distract it by feeding it truffles while Handy and Hefty took a rowboat to the island to rescue the Smurfs stranded on it. When the Truffle Trolls gave chase to the Smurfs across the lake on rowboats, the creature saved the Smurfs by crushing the trolls' rowboat with its tentacles, then sent the Smurfs through an underwater passage that led to a waterfall so they could escape the cave.