The left eye of our MC obtains superduper-vision powers after a freak accident. At first it manifests as the regular see-through vision, but not too long after it starts to include 'eidetic vision' (blatantly giving him eidetic memory). This is all within the first 15 chapters. I fully expect more powers to bloom.
(yes, I said bloom, since I already used manifest).
One of the main things of the MC's power trip is the little tree inside his 'Black Iron Castle' space, which gives him fruits to eat in return for the actions he has taken, consequently giving him substantial power-ups.
He picked up a 'Jindan'. This helps relieves his fatigue and gives him tremendous endurance to keep going, both in practice and actual fights. It also has a few other nifty side-effects, but that's best left for when you're reading the novel itself.
It doesn't appear overpowered or overly useful except for getting our MC started on his journey to become stronger.
(Jindan = golden egg-like object. It's contained within the body. Most chinese novel readers will be familiar with this term.)
And quite frankly it's hardly a spoiler, since it's a well-known reason for any dungeon-like worlds. The gun / firearms don't allow you to harness any powers when slaying monsters in/from the dungeon. So you need to use the so called "cold" weapons, such as swords/axes/knifes etc. It's pretty much the general reason to get rid of any science-based weaponry. So basically any weapon that requires you to exert your own strength is allowed, even a bow. Anything explosive and makes use of chemistry isn't 'allowed' (gun powder / bullet).
On a side note I always wondered about bows and crossbows. Bows I understand, you use your own muscles to align your power and coordination into a succesful shot. But crossbows make use of a mechanism to shoot the bolt. Which isn't unlike a firearm, the only difference is that the firearm makes use of an "explosive device", the bullet. I guess it's the 'chemistry' reason again. Answering my own question, yay.
No need to comment on this spoiler section. I'm just rambling. lol.