Plun-Darr is the home planet of the Mutants. It is orbited by a great many moons from which the Lunataks originate. Not much is known about the world, except that it no longer has its moons, as they now orbit New Thundera.
On the opposite side of the sun that the world of Thundera orbits. It has boiling oceans and scum filled deserts. Being home to the warmongering mutants. Originally it had been a sun dappled paradise exceeded in beauty only by thundera. But the planet suffered from war amongst its inhabitants and the rest of the universe since the invention of the spiked clubs a million winters prior. The world was destroyed at the same time as Thundera.
There are not many details about the world of Plun-Darr in the Wildstorm comics, but at the end of the "Dogs of War" story arc the Mutants were sent back to their homeworld.