The Abyssal Horde takes slaves, and uses their bones to build the walls of their city. Within its ranks are monstrous forgemasters, who crafted a massive blade for their Underlord. Those who meet the Abyssal Horde inevitably face their destruction or enslavement. Dead slaves are thrown into the furnace, possibly to fuel the forges.
Not satisfied with the limited lands of his subterranean domain, Vrogros set his sights on conquering the lands above. Opening a Dark Rift, he sends the Abyssal Horde's legions through the portal to test the nations above, knowing well they may be defeated. Meanwhile, the full force gears for the main invasion below, as Vrogros steps onto the surface himself, preparing to open the rift that will bring his conquering army to the surface world. The horde is evidently secretive or isolationist, as the surface world had never heard or prophesized their coming.
Pudge may have once eaten a member of the Abyssal Horde.