Look at the number of HP mobs and players using the AxisHealthBar add on from AxisCube. There are several types of heart icon designs. There are icons for most mobs.
Select version for changelog:
Changelog
Mob icons: creeper, zombie, herobrine, cheesecat, axolotl, skeleton, cow, pig. Warden healthbar fix
(Edited) it did work however if the custom mob or custom monster has lots of hearts then the hearts goes off the screen which I figure that would happen, if you could make a different version of the addon that just like the 1 in java that work for custom mobs but says how much hp they have in numbers only then that would be very nice, plss do that if you can & you will be rewarded in the future when my world & addon is out on mcpedl
Hopefully this update might fix it