Toby fox the creator of undertale made a 'sequel to it called Deltarune. It is unknown if it is a sequel, prequel, or parallel universe, but it being a parallel universe is the most likely answer. Deltarune has 7 chapters and only the first 2 are released so far. In the second chapter, there is a secret boss who uses pipis as a weapon. Pipis is the name of a clam but in the game, it's a blue oval that hurts you. There are countless memes about the secret boss and pipis. One meme consists of a guy saying "Where's all the Pipis?" and then he walks into a bathroom with a sign that says Pipis room. This is what this meme is about.
