SCP Foundation

What exactly can I use from the mythology and what can I make my own? Should I make it really accurate or should I put my own twist on it (Like my own explanation for why they can do what they can do)?

Should I make it really accurate or should I put my own twist on it

I'd say go with a twist. If what you write up is essentially a rehashed version of classic myths, then the audience might get bored with the lack of unique material. The articles that borrow from mythology tend to be more engaging if they offer a different perspective that the reader might not have considered before; if you write "Norse myth, but as SCP" people who are familiar with the myth involved might predict everything that happens in the article and it'll seem like a stats dump more than a piece of flash fiction.