/usr/lib/libmono-2.0.so is in libmono-2.0-dev 4.2.1.102+dfsg2-7ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libmonoboehm-2.0.so
/usr/lib/libmonoboehm-2.0.so