In a nutshell, the devs will remove nightmare mode Eternity Vault and nightmare mode Karagga’s Palace for Fallen Empire. Unique drops previously found in the nightmare modes will now drop in hard mode. The timed run titles for nightmare mode will no longer be earnable, and nightmare mode achievements will be moved to a new archive section of the game’s achievement screen and can no longer be earned after the expansion launch. In short, if you’re one of those people who has to have every achievement, you’d better get busy!
Source: Forums; thanks Mikey Moo!
