It is not possible to have some pages hidden from the public, so you will run the risk of spoiling your players with information if you put it on the wiki. However you can hide parts of a page with a foldable tag so casual viewers won't be spoilt.

Within a paragraph hide text with  ++ then the text for the link 
that will unfold the text, then the pipeline character "|" then 
the text to be hidden, then ++ and back to normal.

To hide more than a paragraph you have on one line "++++ Title |" 
with Title again being the link text that unfolds the hidden text.  
Then all your hidden text, and you end with a line "++++"

This paragraph has hidden text which you can see when you click on the link .

This section of the page