Please remember that VulnHub is a free community resource so we are unable to check the machines that are provided to us. Before you download, please read our FAQs sections dealing with the dangers of running unknown VMs and our suggestions for "protecting yourself and your network. If you understand the risks, please download!
MERCY is a machine dedicated to Offensive Security for the PWK course, and to a great friend of mine who was there to share my sufferance with me. :-)
MERCY is a name-play on some aspects of the PWK course. It is NOT a hint for the box.
If you MUST have hints for this machine (even though they will probably not help you very much until you root the box!): Mercy is: (#1): what you always plead for but cannot get, (#2): a dubious machine, (#3): https://www.youtube.com/watch?v=c-5UnMdKg70
Note: Some report a kernel privilege escalation works on this machine. If it does, try harder! There is another vector that you should try!
Feel free to contact the author at https://donavan.sg/blog if you would like to drop a comment.