Minecraft – Do murderous zombies take all your loot

I have invented a solution to this problem using a mechanism to apply one tick of lava damage. It occurred to me that a tripwire could be placed immediately above lava in order to remove it (using a dispenser) as soon as a mob hits it, thus preventing the mob from continuing to swim in it. Doing this for the water as well as the lava means that no acceleration is needed to make sure the mob will fall down, so the whole mechanism is only a little bit of extra height above a standard fall-damage trap.

Build details, from top to bottom:

• The zombies are pushed by water into the drop pipe. I don't know how important the length of the upper section is.

• The water and lava mechanisms are identical:

  • Each dispenser contains an empty bucket.

  • All pistons are sticky.

  • The tripwire above the fluid is the input to the left (in first image) piston monostable (rising edge detector), which causes the dispenser to remove the fluid into the bucket. The monostable ensures that the tripwire input will not interfere with the second fluid-restoring pulse.

  • Behind the dispenser is a comparator followed by 2 blocks of redstone wire; this detects the dispenser having a lava bucket (which counts as 1 stack) instead of an empty bucket (which counts as 1⁄16 stack), and triggers the right piston monostable to remove the fluid. In the event that the state of the dispenser gets reversed, this circuit will simply not generate a pulse, thus correcting the problem.

• Below the water block is exactly 19 ½ blocks of empty space (counting the sign) down to the fall-damage landing platform.

Results: When the zombies hit the platform, a few still take 2 punches, but most of them take 1 punch to kill. I have successfully operated this mechanism in my survival world fed by two zombie spawners.

Glitches:

• The amount of damage done is not completely reliable.

• It is possible for the dispensers to get inverted (resulting in zombies falling on fire, without taking any lava damage, or from the wrong height). This latest revision with comparators can self-correct this problem, but it still may result in an occasional zombie with the wrong amount of health. (I have also seen a dispenser completely fail to respond to pulses, so I suspect there is a Minecraft bug involved.)

I know it can be hard to build mechanisms from screenshots, so if you would like any further explanation of other camera angles, feel free to ask me to add them.

The baby zombie you cured before was a baby villager zombie. Normal baby zombies can't be cured.

Here are two adorable baby zombies, one a villager and one a non-villager. I've hit them with a weakness potion and offered them both cookies golden apples. Only the baby villager zombie accepted the apple, as you can see by the dark red spirals around that one compared to the black spirals around the one on the right:

While I was writing this answer up, Harold (the baby villager zombie) had a complete recovery and is now ready to grow up and become a productive member of testificate society:

Technical details

The NBT data for zombies contains two relevant flags: IsBaby and IsVillager. A baby villager zombie is exactly like a normal baby zombie except that it has IsVillager: true while the normal baby zombie has IsVillager: false.

Since the code for curing tests for IsVillager: true, the curing code is skipped if you try to cure a zombie that has IsVillager: false. This makes normal baby zombies incurable.

Where did the baby villager zombie come from?

It's commonly believed that baby villager zombies can only be created by a zombie killing a baby villager. I thought so myself, but this is apparently not true!

Digging through the decompiled game code provided by MCP, this is the line that controls what kind of zombie spawns:

par1EntityLivingData1 = new EntityZombieGroupData(this, this.worldObj.rand.nextFloat() < 0.05F, this.worldObj.rand.nextFloat() < 0.05F, (EntityZombieINNER1)null);

Notice the two calls to rand.nextFloat() < 0.05F. Those are what ultimately set IsBaby and IsVillager. The first call sets IsBaby true in 5% of zombies, while the second call sets IsVillager true in 5% of zombies. Notice that neither depends on the other.

The spawning probabilities in combination:

                   | Non-baby |    Baby
                   |   (95%)  |    (5%)
-------------------+----------+---------+
Non-villager (95%) |  90.25%  |   4.75% |
-------------------+----------+---------+
Villager     ( 5%) |   4.75%  |   0.25% |
-------------------+----------+---------+

So in summary, the chance of a zombie spawning for each type is:

Zombie type      Spawn chance (%)
-----------------------------
Normal            90.25
Baby               4.75
Villager           4.75
Baby Villager      0.25

Your baby villager zombie was likely a very rare 0.25% zombie spawn. You were very lucky to find it and catch it!