[mockingbird]

Thanks for the suggestion, but I don't think that's it, as it has the same permissions as all of my other saved games:

ls -alt@ late_marignon.trn
-rw-r--r-- 1 username 502 94922 Jul 16 13:58 late_marignon.trn

I removed (or so it seems) the extended attribute using
xattr -d com.apple.quarantine late_marignon.trn

I also tried grabbing the attachment again and just opening it directly with dominions, to no avail.