User blog comment:Varzan Deodinm Beldinm/Search and Destroy: Ooh, Oobleck you're Amazing!/@comment-10380701-20141003002012/@comment-3146930-20141003003827

I'm still going with a theory about a type of Gravemind, like from Halo 2-3. The original war with the Grimm defeated it, but it went into hibernation and humanity erased those events from history or where lost in time. However that monster's hatred for humanity still influences the current Grimm. Once it awakens, it will take control of all the Grimm and organize them for a full scale battle. The Grimm now are like the Flood from the original Halo, still dangerous but leaderless and acting as individuals.