This mod requires LLibrary. You can download it right here

Life Guage is a mod that displays the current health of a mob. If the mod isn't installed on the server, potion effects will not be visible. It's not required to be installed on the server, though. A server can also disable the mod for all the users connecting.You can see the current hearts on the name tag and the total hearts on the black bar.A name tag is always preferred over the normal entity name.