Laura "lelo" D. Arrowsmith Deddens Gerard
Pearland (near Houston)
I have both the Libellud and the Portal Games versions of Hidden Signs.
And of course the ghost screen for the polish version, that was already in the libellud base game.
I ordered my Polish version directly from Portal Games. It did come with 2 screens for use by the ghost. However, they do not fit in the expansion box so I'm not sure you would get them unless you order directly from Portal.
AND!!!! They are nothing like the Libellud screen. There are no slots to put the cards in. All they do is hide what the ghost has put on the table like any other player screen. I'm looking for a picture.
Also, my Polish copy came with 43 vision cards and while most are the same as the the Libellud there are a few differences. See here for discussion of differences in vision cards with pictures: Does every version have the same vision cards?
Lastly, the Polish version comes with a mini expansion that is not in the Libellud version. It consists of 3 cards and rules. The cards are identical on both sides.
English translation of the rules here: False Lead Variant Rules EN
But to answer the poster's question. You can combine it with the Libellud edition of Mysterium if you don't mind the backs of the cards being different and that the ghost cards are a different size. Doubt you would want to use the vision cards as those are mostly repeats. But unless you have worn out the replayability of Libellud version, there really is not need to have this one too.