This is the boss for the Special Episode In the Future of Darkness.
Along the way through this dungeon, players will encounter as many traps as they did in Sealed Ruin.
The geography of the entrance to this dungeon is very similar to the geography of where Wigglytuff's Guild set up camp for their expedition earlier in the game.
This is referenced in the hero's dialogue. When the player reaches camp, he or she notes that it feels like he or she has been there before. The protagonist later remembers this feeling at Dusk Forest.