1.
Level 41, aka Grandma's House, is a relatively-small liminal space, only consisting of small rooms and corridors from the 1980s.
I'd remove the word "only", will have better flow.
2.
Most of the time, it's
Correct "it's" to "its". Check the article for every "it's", there are a few of these.
3.
and wetness all-throughout the level.
Just "throughout" will work better here.
4.
Every step you make in the house must be light, as the floorboards are extremely creaky!
I don't know if making this an exclamation is a good move, I think it would read better with just a period.
5.
window will ALWAYS be locked, and Grandma will come stop you. She has senses like a bat, or a hound…
Consider removing the all caps from "always", for the same reason stated above. I think the last phrase would do better if you just selected one; either the bad or the hound. I'd select the hound, given that hounds return in this story a little later, just for thematic consistency.
sources of Voltaic Urchins in almost very crevasse of Level 41.
That "very" seems like it should be "every"
This room is NOT safe, so use at your own risk. Even though Grandma has never been spotted in this room, Grandma knows the in's and out's of her home!
This line repeats the information given a few sentences before, that Grandma has never been spotted in this room. I think I'd go back and remove the first sentence mentioning this, so that this sentence plays fresh.
it's unknown why as this room has the same moldy and wet feeling as the others.
I think conceptually, this is a bad decision. It is not uncommon for whole houses to be infected with invasive types of mold when they feature them, so it doesn't make sense why they would be unsure as to why several rooms had this feature.
Grandma's domain. The room resembles an elderly-woman's room from the 1990s,
Since we already get the idea that Grandma is an elderly woman, I would remove that part of this sentence, and just say that it features furniture circa the 1990s, and so on.
Nothing notable has been found in Grandma's room, except the only known exit to this level.
This reads strangely, consider changing it to something like "Besides the exit, there is nothing of value or note in this room."
The UNCB has tried multiple times to setup a basecamp on Level 41,
Should be "set up"
