/usr/lib/games/doomsday/plugins/libhexen.so.1.0 is in doomsday-common 1.15.7-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/games/doomsday/plugins/libhexen.so.1.0.0
/usr/lib/games/doomsday/plugins/libhexen.so.1.0.0