PSA - Conserving health in Nightmares and Dreams

If it's not a forced fight, then just run.
Also - always run in an anticlockwise direction on the very last arena section,
that way you'll be synchronized with the rotating bars

The Seraphinx's Heart attack helps a lot here. If a couple of you are using it together you can get the monsters dropping a fair few hearts! You really need to crowd control too. Shivermists and Pulsars are a must. :P
Also, knowing when to get the heck out of there is important. Its easier if you have a team that is communicating. :P
We did a run through for our community channel if anyone wants to know what they are getting into before running it.
It can be found here:
https://www.youtube.com/watch?v=qNEJB58wXLU
It's a neat mission over all. Pretty challenging in areas but it's just nice to have new content really. Arkin felt a bit differently, I can see his points but personly I enjoyed the new missions. :)

DR is really good aainst void gremlins and wolvers, since they are always on your tail. also a good placed DBB can clear crowds, and mist bombs are a really neat tool to bring. don't bring vortexes, there are too many enemies, they will hit you when you start charging.

I tried bringing Stagger Storm, when I realised something. Are Void Zombies immune to minor stun?

Are Void Zombies immune to minor stun?
My shield bash says yes.

I just run around the perimeter, shielding, shooting; slashing anything that comes in the way.
I survive longer, but not long enough to survive.
sigh...
Stupid void souls....
Curse those high damaging turrets...

Huh? High damaging? They do less than 3 bars of damage if you're wearing the right gear lol, and that's even if they break through your shield in the first place.

Void Turrets are the strongest argument for Normal defense the game has ever seen.

Yeah, pure normal. So don't complain about how much damage you're taking if you're equipped with glass cannon/offensive armor.
So any plate mail, and to a lesser extent, Azure Guardian, works wonders.
For shields, you'll be wanting Ancient Plate/Ironmight Plate/Volcanic Plate/Grand Tortoise, and to a lesser extent, Heater Shield/Aegis if you don't feel confident using SSB or BTS.

Do vortex bombs work on lost souls?

Easy to forget exists if you - like me - never see a need to do it: buy a Vitapod and Health Capsules from Basil in the mission lobby. Having 12 more hearts really helps a lot.
If you're the patient type (and moderately good at prolonged defense): in the penultimate, second to last, arena on depth 27.. dont step on the 1st small red button, keep killing the one monster that spawns, some will drop hearts. (The downside of this part is.. failing to defend - notably from souls and nearby turrets - can easily take more hearts than you had won back.)
A tetra-heart pendant and having your sprite use its strongest health boost perk help tremendously.
On Elite, I buy 1 health capsule from Basil. 500 crowns is a steal since it pretty well guarantees being able to win. On Elite I'm typically making around 1400 crowns for the run, so even with buying the capsule it's a net gain...and crowns aren't the real goal anyway. All about the rarities.

Anyone with a seraphynx, use the heart attack skill at the beginning of every arena wave
P.s. be ready to deal with idiots who doesn't use it AT ALL and who try to use " it has a cool down" as an excuse, we all know it doesn't have a 30 minute cooldown

My crown pool is starting to see a bit of dipping concerning purchase of vitapods... I also kind of regret not having a Seraphynx with Heart Attack maxed out on the ready.

The final battle really encourages knowledge about "sonic-mode". My primary way of staying alive there is only having 2 pips of health and trying to keep at least one heart on the battlefield. Since I do it solo too much already, I need all the damage I can get so I often use my seraphynx for their laser opposed to heart attack. Since I run counter-clockwise around the whole place enemies tend to group up in the middle, so my seraphynx is very happy zapping all the void enemies that gather there.

DaN is not bad with some Tortofist charge. The backward slide and minimal animation time (for quick shielding) on the charge makes it great for retreating and dealing damage. Shield up when it's not safe, and then safely loose a Tortofist charge whenever you feel like it. Tortofist charge is also helpful for clearing space of those pesky spirit-things (great for chaining into something like a Slug charge).
For the handful of runs that I've done so far, Mighty Cannon and Iron Slug feel good to use.
I had Mighty Cannon and Iron Slug on my first encounter with the last depth (which I solo'd). Ended up using ER and a spark because of lagspikes...
Anyways, soloing DaN is more reliable than doing it with a team. In solo, you just know all the enemies are coming after you, and not running across the map chasing your teammate and inadvertently cutting your path off, whereupon your teammate dashes and then they all attack you.
@Fangel:
Yeah... don't really need Heart Attack. It's nice to have, but I just bring along my fully leveled Drakon. I feel like Sonic Mode trivializes this fight. In most other fights in the game, you don't have such a readily available source of hearts. In all the other fights, you get a small chance of a couple hearts from the few respawning enemies... but here in DaN it's just some several enemies to kill to regain Sonic Mode.

If you have a Seraphynx and you need extra health before the big fight in the final stage, then you may want to hang around the button puzzle arena right before that. Once the path forward is open, use Heart Attack whenever it's off cooldown and let / help Vaelyn kill monsters while you run away from any danger.
As long as you avoid getting hit (you might want to kill the lichens when they show up to avoid a random needle), you should be getting a lot of hearts for each Heart Attack. You can keep doing this for as long as you like before hitting the last party button.
I've found this is (kinda?) helpful for solo runs. Also, I'm not sure how effective this will be without relying on Heart Attack.

As a grand tortofist and iron slug user I can confirm that the combo qwez described works great
Without a turtle gun providing a wall, I've found the Iron Slug to be disastrously awful in the arena fight. Only the charge is very useful, and getting charges off without getting pimp-slapped by something is something I've never been able to manage. The movement delay also really screws up the timing of moving around the spinning orbs at each corner. Plus since the monsters tend to clump in the middle while chasing you, the charge loses out on about half of its damage ticks just reaching where the monsters are. I've been equipping my Iron Slug for (slowly) heating it during these runs, but I long stopped using it.
So far, the best weapon I've found for the arena battle is the Dark Briar Barrage. Then just bring one other weapon to deal with the lumbers and lichens.
I own a Sera, I only use the Heart Attack on final arena when the wave is spawn and already taken some sort of damage or else Heart-Atk-Effects will run out. Run counter-clockwise and charge (IronSlug, DarkRetribute) to the center like being advised in different thread.
Solo is much easier with Slug and any fast sword. Or party with trustee friends :> because random party is full of surprise.
In early level, just run, don't bother talking or fighting. If you die because you are so nice to explain to new player what to do then it's your fault, Noice-guy
[No personal attacks please].

@military
Was that comment aimed at someone in particular or just to any reader?
P.s. your English is fine as long as its readable, which it is
The actual way to handle this fight is actually quite interesting. This battle requires control of the field and you can't just go aimlessly blowing everything up like usual. (well you can, but four turrets firing at you hurt.) This fight deems patience and well timed charges, shots, and explosives to make it through without killing everyone.
I've been able to solo the entire thing on Elite with almost no damage (curse you Slimes) by selecting a single corner and just sticking to that entire corner while preventing myself (and the Swarm) from accessing the other sections. This makes the arena much less of a hassle and just requires good coordination with your group to prevent the rest from opening.