LifeGauge Mod 1.8.8, 1.7.10 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.
How to install LifeGauge Mod 1.8.8, 1.7.10
Download Links for LifeGauge Mod 1.8.8, 1.7.10
For Minecraft 1.7.10