The latest Guild Wars 2 patch notes contain information on Nightmare, Professions, etc.
The nightmare settings are:

The boss-to-boss exposure was reduced after the resistance bar was broken.
Endless Ensolys tortured by the Magic Band can no longer be destroyed twice in a row during the phase transition.
Certain professional skills have been adjusted, especially the engineer, ranger, avenger, thief, and warrior. For example, it is a change of engineer.

Purity of Purpose: Fixed a bug that prevented this feature from affecting teasing.
Objectives: The description of this function has been updated to ensure accuracy.
Burning Explosion: Due to its properties, this ability is now considered an explosion.
Eddy Current: For functionality purposes, this ability is now considered an explosion.
World Polish also applies to this patch, which includes:

Mounts are now available in the main hall of the North Eye, but flight altitude is subject to restrictions.
A repair anvil has been added to Eye of the North.
Map markers have been added to the Achoura Gate of the North Eye.
Fixed a bug that prevented multiple NPCs from appearing in Cragstead.
Fixed a case that resulted in a stalemate in the search for forged steel, resulting in "Swani's son defeated in time and his proven ability to ash."
Fixed a rare bug that caused the event "Participate in Ranoah Combat Training for Devouring Cannon TT6-B" to crash during a forged steel mission.
Fixed a bug that prevented players from engaging in Vishin's sniper activity to earn gold medals during fake steel missions.