How NOT to Summon a Demon Lord

Will Diablo be able to conquer the dungeon he himself created?!The High Priest Lumachina has been afflicted with a curse, and Diablo's only way of saving her is by reclaiming an item he once obtained in the game Cross Reverie. His next challenge: a dungeon that has claimed the lives of many brave adventurers... But his confidence isn't misplaced, for it was he who designed that very dungeon! Even when facing off against a supreme dragon, Diablo never falters, just like a true Demon Lord! "Heh, you think yourself a God with a mere level of 140? Don't make me laugh, you overgrown newt!"At the same time, a Fallen heralding the return of the Demon Lord appears in Zircon Tower...?! Will Diablo be able to conquer the dungeon he himself created to retrieve the cure and make it back to defend Zircon Tower in time?!