In 1.8 it is possible to manipulate ender dragon health using the /entitydata command so it looks like it is losing health. (As can be seen in this video at 1:28:)
In 1.9, however, they have made it so that the ender dragon boss health bar does not appear unless you summoned it properly using the creeper-face clay structure, so this is no lonnger possible. (You might ask, "What about the wither?" Well, MC-83571 is preventing the wither from being used, too)
So my suggestion is that proper support for custom boss health bars gets added through the use of a /bosshealth command.
The syntax would be:
/bosshealth entity <selector> <name> <color>
This would function as per normal, by making it so the boss health bar that appears would be full when the entity's health is full, and at half when it is at half health. A boss health bar for entities would disappear upon the entity's death.
keep this going guys. Make people aware of this issue. Current boss health bars are broken... Bug MC-83571 We need something like what is in this thread or in my reddit page to allow for Map makers to continue to make epic boss battles in maps. Show your support!
Rollback Post to RevisionRollBack
Creator of The Doomed Series! My Newest Map Is: Castle of Doom! Link: Here