I was rereading old chapters and came across chapter 12 the chapter in which a hollows sins could not be cleansed because of the crimes he did as a human so when ichigo slayed him the gates to Hell appeared and took the hollow to Hell
.....then it hit me add Hell to the game as a new training ground but not for everybody it should be that you have to be a certain level to gain entrance to Hell like atleast lvl 80 and the NPC's in hell should be really strong and look like holows on crack (giant, kinda redish in color, mean) but why stop there? In the chapter you see a giant fiend pull the hollow into Hell so i was also thinking of adding this fiend deep within Hell kind of like the boss it'll be uber strong almost unbeatable for one person alone.