Also known as: 闇の泉
A major plot element in Deltarune. They are pillars of Darkness (sometimes appearing to be Blue Fire, and manifesting in the Light World as Black Smoke) that give the Dark Worlds form and fuel their existence.
According to Ralsei, Titan (Deltarune)s are born when too many Fountains exist, or (as shown in Chapter 4) when one is created inside of another Dark World.