In Season 1, Cloud was absorbed by an interdimensional fissure that warped him to Oblivia. It appears as a dark, gritty area with a deep red sky. Orbiting the main planet is a parallel version of Cloud’s Observatory that is implied to have been led by Dark Cloud.
In Season 2, Switch, Megar, and several others traversed Oblivia to revive Cloud. Along the way, the group explored neighboring planets Redblaze, Aquachord, and Softfreeze. It is unknown if the term “Oblivia” refers to the main planet, the dimension itself, or both.
From Season 3 onward, Oblivia is never visited again. It is implied to have been destroyed by the death of Zerospace. In the finale, Spectra left Cloud’s Observatory to “fix up” Oblivia. What exactly this entailed is not known.