"As If": This was added to the FAQ (v.1.7, March 2020) and then amended (v.1.8, October 2020). You can read the October ruling on the ArkhamDB rules page here. (I'm adding a hyperlink rather than retyping the rules in case in future the ruling is changed or amended - at that point, the rules page will be updated and all ArkhamDB FAQ entries will link to the correct ruling.)
Q: I have a question about Unhallowed Country. Does its second line of text remove traits from allies as well, including the Ally trait itself? I compared the language on this card to Mind Wipe, Stubborn Detective, Threads of Reality which all have "except for Traits" language. A: Thank you for bringing this to our attention. Unhallowed Country should have been given a wording such as Mind Wipe, where the text box is treated as blank except for Traits. Please apply this same logic to Unhallowed Country; your Ally cards will remain Ally cards for the duration of the ability.
Revelation - Put Unhallowed Country into play in your threat area.
You cannot play Ally assets. Treat the printed text box of each Ally asset you control as if it were blank.
Forced - At the end of your turn: Test (3). If you succeed, discard Unhallowed Country.
Dziedzictwo Dunwich #88. Dunwich #1-2.
FAQs (taken from the official FAQ or FFG's responses to the official rules question form)
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