Mumu-Obscura was a militarily contested and strategically significant world in the Eigerson-48 star system, until a group of warriors called the Reapers exterminated its population and poisoned its resources.
IDW comics continuity
The Reapers' attack on Mumu-Obscura was described by their leader, Deathbringer, as an attempt to "cauterize one of the universe's many bleeding wounds". They claim to be in some sense serving a greater good, trying to end all war, by razing planets which are likely to inspire many future battles and lost lives. Their work on Mumu-Obscura was very thorough. Not only was the entire biosphere incinerated, but the world's atmosphere was partially ejected into space, the planetary crust "contaminated" in some way, and all vestiges of the now-extinct Mumu-Obscuran civilization's infrastructure were destroyed.
After the Reapers' attack, the Decepticon Sixshot arrived, searching for the Terrorcons, who had been sent to bring Mumu-Obscura under Decepticon control. Sixshot found that the Reapers had captured the Terrorcons, seemingly to use them as bait to lure him to the planet in an attempt to recruit him into the Reapers. He declined this offer.