User blog comment:Kogath/Monster Hunter XX Discussion/@comment-6050823-20161105095739/@comment-17735225-20161105133750

If I understand correctly, in the japanese version of the game the quest to unlock the crimson blos armor is the fight against one horned demon king Diablos. So in a way, One horned demon king 'is' Crimson diablos.

And I'm pretty sure that Massacre Demon Diablos is created a late version of what Crimson Diablos is supposed to be.