This is by far one of the worst DLC's i've ever played for any game in my life. I am so angry after playing through most of the story; the enemies are COMPLETELY unbalanced in Nightmare mode.
There is an enemy zombie with an elemental on its arms(think the necro mages from Diablo 2) and they can throw a straight projectile. These projectiles do more than a third of your health, they flail their arms like Virals throwing on with each swing. They usually spawn in groups of four to five with HORDES of "virals", "thugs", and "rais thugs" (that's what I'm calling them, they are reskinned to look like skeletons and zombies.). These stupid "mages" are immune to almost every parkour move in the game, they cannot be stunned, you cannot fast-kill them. Seriously?
Then there is the shield skeletons, this enemy is just fucking stupid. They have a perfect-block shield raised at all times where any attack you do "whooshes" (most of the time, sometimes it has a clank for hitting the shield but it usually just whooshes in thin air.) Now the way this stupid enemy seems to be programmed is that it's "blocking" works in a slight AOE around it, the problem is if there is 2 of these stupid fuckers clumped close together, you have to get lucky enough to make them both attack at the same time to make them vulnerable or else you can't damage them. They can also "defend" other virals and shit swarming you. It has an upper-cut attack with its mace that knocks you down, and does like 50% of your health, this is basically instant death because it is able to do a follow up attack even if it's the only enemy left.
Insane amounts of these enemies swarm you at a single time, like A LOT, far more than anything in the base game. You would have an easier time fighting off a few volatiles than deal with this stupid shit. DO NOT ENTER THIS MODE IF YOU HAVE LEGEND POINTS TO LOSE, YOU WILL ABSOLUTELY FUCKING DIE LIKE 5 TIMES PER ROOM.
There's a lot more to be said on how ridiculous this mode is, but to summarize it as quikcly as possible I'd rather fucking play Dying Light 2 to completion 5 times in a row than revisit this DLC. If you are not on the definitive edition I highly recommend you skip this one, it's a massive waste of 10$. I'd rather walk outside and throw a 10$ bill in the air than buy this again. Holy crap, the negative reviews were not kidding.