Remember that you do NOT need to worry about completing this, if you are a newer player and don't have the hones/gear/chars leveled needed to clear, you can wait for the Torment Dungeons to open up again next month and complete both this one and the next one then.
Event Start Date: January 2
Event End Date: ???
All Information is taken from a mixture of Reddit/Spreadsheets/Kongbakpao Site.
Most, if not all info for the event (Commentary/Event Info/Ultimate Abilities was directly copy/pasted from it, so all credit to the site for that especially!) comes from this site: http://ffrk.kongbakpao.com/nightmare/
What is a Torment Dungeon?
Torment Dungeons are a new type of dungeon where you face very tough dungeon fights against waves of monsters and a boss round in order to get Job Motes in order to unlock the useage and gain Record Dive 6* Abilities.
Your stamina has to be at minimum the level the dungeon requires in order to enter, so if a dungeon had a 60 stamina requirement, you obviously need 60 minimum to enter.
Do I lose Stamina if I lose?
No, if you fail to win the dungeon, you get your stamina refunded just like as in Multiplayer.
Can I mythril restart the fight if I lose?
No, you cannot, you lose and you're done.
Difficulty Tier is D200/D250, so about on par with Mote Dungeons, with D250 being more close to how Mote Ifrit is.
Is it just a boss fight?
No, you have to fight D200/D250 level tier 5-7 waves of trash BEFORE you even face the boss, so make sure your abilities are well honed, use BSBs too if you got them, will go a long way to conserve ability useage.