As of 13w16a the custom health option doesn't work anymore.
How to reproduce,
-create a custom spawner using NBTExplorer or the NBTEdit mod
-make the spawner spawn villagers with the TAG_Short 'health' set to 0
-You will see the villagers will stay alive
in 1.5.1 and 1.5.2 the villagers will actually die. So this bug will break all pre 1.5.2 maps.
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This seems to be a bug fix rather than a bug. If you set health to zero, it's health is ZERO, and when it's health is zero, it should logically die.
That was the whole point, you can spawn villagers and make them immediately despawn. That's usefull when you want a redstone to get powered only when someone is on a certain position. The villager would trigger a pressure plate and despawn. Now I'm going to have to use items. That will work just fine except item spawners will create glitched stone items once, and that's just annoing. Plus this breaks all pre 1.5.2 maps
But would it cause too much of a problem? Normal Death animation is about a tick for most, I don't think it should cause too much delay...if you spawn the villager one block above the pressure plate it should work.
Edit: Also, you can edit the Death animation manually with the NBTTag "DeathTime". Try setting it to 0 ticks.
Hmm I'll try that. But I think you will hear an annoying falling to death sound. Plus this doesn't take away that all pre 1.5.2 maps using this will be broken.
Assuming they die in midair, you wouldn't hear a fall sound, would you? Or, alternatively, you could use a monostable.
No, they don't die in midair. That's the problem, they don't die when you set their health to zero in the spawner. No matter what NBT value you set in the spawner, the villager will always spawn with 20 health.
Wait, I think you pulled a switcheroo with the bug report on me, I thought the bug was that they died, not that they lived. O_o
Well, whatever, the monostable (I think it's that kind of circuit, the one that generates a pulse from a continuous output? Because it's the flip-flop that creates a continuous output from a pulse, and you want the opposite of that) should still stand up, though I'm not sure why the villagers don't die.

Dinnerbone's comment on MC-13276 may be related to this:
Technically speaking, mobs with higher health than their max is a bug caused by a "health = max" line in our code that should be "this.health = max", but we've let it slide because it's cool functionality.
I'll fix this in 1.6, but there'll be a better way to do all of this 🙂
Still in 13w21a
Jesper....using sethbling's filters....make the MOB health 0. Then spawn a mob with 0 health.
yeah, everybody is saying that to me, but I don't see why it wouldn't work with an ingame NBTedit mod and it would work with sethblings filter. But I'll try it anyway.
Ok I tried it and it didn't work, but I think might need to change this.

Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
(Automatic Message)
confirmed for 1.6.2
Added two schematics - one defines a Zombie's Health and HealF to be 200, and yet it still only takes 5 hits of a wooden sword to kill. The second one also defines the zombie's MaxHealth attribute - this worked during the 1.6 snapshots, but as of 1.6.2 the zombie immediately dies upon spawning.
Clearly, neither method works anymore, whereas both did in the snapshots (I'm not sure how early). There are no replacement methods or new tags.
This essentially renders the new Attributes system and the existing health system unusable for mobs.
So changing the attribute generic.maxHealth doesn't work either, I didn't test it because I don't need it any more. I use items with age set to 5999 to trigger redstone now.
I'd recommend experience orbs with a value of 0, if that works - no accidental pickup if the player is too close to the redstone.
Sadly, there's no practical workaround when you actually need a mob with above-average health, i.e. for a boss fight. The closest approximations I've found are Resistance and Regeneration status effects, which carry their own limitations. From what I can tell, even items that adjust their max health won't actually work.
Oh that's a good idea actually. Well I'm going to leave it the way it is now because usually I put the pressure plate more than 15 blocks away from the player so you can't hear the sound.
Jeb said this is changed because of this.health or something, but I don't get why this was changed in the first place. I understand why you can't set a custom UUID that's because other wise you will crash the game, but health and rotation just doesn't make sense.
Updated zombietest3 - zombies have custom health in this version. I'd like to thank my friend Arkantoswar for being able to produce a functioning custom health mob spawner - it seems mine had a silly mistake due to the wrong tag names getting copied.
Zero health instant-dying no-item-or-experience-dropping mobs are also possible, if the attribute sets the base health to zero - this is demonstrated in zombietest4.
From what I can tell, this can probably be closed as "Invalid" or "Works as Intended", as Dinnerbone said the method to create custom health mobs will change in 1.6 (as it has). As long as it is possible in some reasonable way (which it is), it doesn't really seem like a bug.
thanks!
rotation however MC-15511 still doesn't work :/
Can a mod close this issue?

Sure.
relates to MC-15511