/usr/lib/mono/4.5/Npgsql.dll is in libmono-npgsql4.0-cil 3.2.8+dfsg-10.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mono/4.5/../gac/Npgsql/4.0.0.0__5d8b90d52f46fda7/Npgsql.dll
/usr/lib/mono/4.5/../gac/Npgsql/4.0.0.0__5d8b90d52f46fda7/Npgsql.dll