After i died in the darkness and wanted to retrieve my stuff, i was just scared enough to sacrifice my dark helmet and dark armor to get the job done. and what do you know.. the dark helmet makes you take MUCH less damage from dark enemies and even the tentacles. you barely even bleed. no more 1 hit deaths.. so much easier.. just equip the dark helmet that you need to buy from the shop at level 6 and i promise you the darkness will be much easier.

that said you will still need to use two skills - lantern pointing and dodging.
point your lantern against the tentacles when they block your way.
PRO TIP: while pointing the lantern keep moving with your dash instead of walking slowly

and of course don't dwell.. its still isn't meant to be played like the rest of the game. you need to move fast between one crystal to another.

dropping gems will give you a small safe area for a bit of time, enough to look at the map, pick up stuff, putting bombs, loot your body and the rest..

be sure to bring bomb arrows, they don't require the use animation like the bomb. you can also stack 4 of them instead of 1 bomb and they blow the rocks just the same.

be sure you coming there well equipped, you will need at least 5 stews and like 200 crystals to feel safe and not stress about it, sure you can do it with less using the helmet but why.. just make a quick run lvls 1-3 and come with plenty of crystals so you can spam the lantern and not worry about it..

also you will need a good stocked pocket, you will have to get into the pocket between each floor and refill. make sure you got good stuff there. you want bandages, crystals in case you will run out somehow, bomb arrows! a lot of food and water, since there are basically non in those levels (another pro tip is to take some blue elixirs since they lock your hunger for a few minutes).

on floor 17 you can find a room to the left which contain a stronger, faster sword. you will need 2 bombs/bomb arrows to get through the door.

another tip, when you start the darkness i recommend you put your spear and hammer in the pocket, they will not be needed and the spear is very important for early surviving when starting a new run, so if you die just take the spear from the pocket, go through 1-3 and buy some items, collect some bandages and stews, again put the spear back in the pocket and go for a rescue mission for you body.

i hope this guide will help you down there.