Retridosa is an alien exoplanet in one of the outermost orbital rings of the Shattered Islands solar system. In fact, it is one of the three infamous worlds to be covered in a dark atmosphere that cannot be scanned through.
In this case, it is a cave planet that is mostly covered in rocks and Energy Crystals, and the weather patterns are so messed up that electromagnetic storms are constant on the surface areas and only spaceships with specialized equipment from the Space Bat Federates can enter and exit the planet without suffering from an EMP and crashing immediately.
The bats are very adapted to this world's underground area, able to fly through the vast tunnels and see with less need of light. Despite this, the glow of energy crystal clusters do not entirely eliminate sight.

Though a Bat is Melancho's normal form, becoming a Mole allows him to better dig through ground areas. He may look bulky but he's actually pretty fast while digging. He can use it most effectively on this world, even if some areas like the Bat City requires flight capabilities.