User blog comment:Jopjopjop/Volume 20 Spoilers/@comment-177.142.210.225-20151110133920/@comment-120.164.45.195-20151111173949

12 heinous criminals called Malebolge, demons originally from Dante Inferno.

Just my theory though, but Euclid being imprisoned and even Riz being dead might be a ploy to release them. Again, it's just my speculation