This was an event Jude had not known about when the Experiment began. He had only learned of it after facing it directly and dying more times than he could count. When the imps started to appear, an entrance leading to an imp den would open. Whoever cleared it would receive various rewards. If the cave was large, the testers usually called it a dungeon or a labyrinth.
But that entrance...
"It looks a lot like the way I get to the hills."
Perhaps the place the imps came from was the same world his hills were in. He would leave that for later, though, and focus on preparing to fight the imps in reality. Jude went through his notebooks and checked all the materials he had hoarded since before the outbreak. He was thinking of telling the studio group what they would need and how to put up a proper defense.
"Imps are stupid to begin with..."
