Head

Mob heads are decorative blocks. There are five variants of mob heads: Skeleton, Wither Skeleton, Zombie, The Player and Creeper. The Wither Skeleton variant is a rare drop from the respective mob, with the other heads only available in Creative mode. As of 14w30a, all heads can be obtained.

Obtaining
The Wither Skeleton skull is a rare drop of Wither Skeletons. All heads except the players' can also be obtained by the respective mob dying due to a charged creeper explosion. Obtaining a human head with the same texture as a specific player's head requires /give, and is achieved by changing the NBT tag of SkullOwner to the player's username.

Usage
The main use of heads is for decoration. They can be oriented in 16 different directions on top of a block, and 4 directions on the sides of blocks, similar to signs. They cannot be placed on top of each other.

The player can also wear heads as disguise, similarly to pumpkins. This will only replace the first layer of the player's skin. If the player has a second layer over their head, it will still render over the head (this also applies to Zombie Pigmen wearing heads). They can also be used as a decorative disguise, using dyed leather armor. Occasionally, another mob may pick up a skull and wear it just as the player would. This is common when a wither skeleton drops a skull next to another mob in the Nether. The only mobs which can wear the heads are the Skeleton, Wither Skeleton, Zombie, and Zombie Pigmen. Other mobs can only wear heads when spawned using custom spawners via.

Heads are not able to be pushed by pistons, as they have tile entities.

Spawning a Wither
Wither skeleton skulls are essential for spawning a Wither. To do so, place 4 soul sand in a vertical T-shape, then place three wither skeleton skulls on top. The orientation of the skulls does not matter.

As a crafting ingredient
Heads are used in the crafting of Firework Stars and Banners. Firework rockets crafted with said stars will have an explosion shaped like a Creeper face, regardless of which type of head was used. Banners crafted with heads will show the respective pattern on the banners itself when placed down.

Player Heads
Human heads have an extra usage for map makers, they can be given NBT data (as shown here) so that they appear with the skin of any Minecraft account. This means if you know that a specific account has a head which you want to display, you can edit the NBT data to make it appear. The command to give yourself a head skinned as another player is, where  is the name of the account of the head you'd like to use.

Mojang has created a number of accounts with specific skins, so that map makers can use common heads without the risk that someone will change their skin. These accounts have names in the format, for example   is the name of a Minecraft user with a Zombie Pigman head. MHF stands for "Marc's Head Format". There are also a few blocks and "bonus" heads, for more variety.

The following names/heads have been made available:

Mobs:
 * MHF_Blaze
 * MHF_CaveSpider
 * MHF_Chicken
 * MHF_Cow
 * MHF_Enderman
 * MHF_Ghast
 * MHF_Golem
 * MHF_Herobrine
 * MHF_LavaSlime
 * MHF_MushroomCow
 * MHF_Ocelot
 * MHF_Pig
 * MHF_PigZombie
 * MHF_Sheep
 * MHF_Slime
 * MHF_Spider
 * MHF_Squid
 * MHF_Villager

Blocks:
 * MHF_Cactus
 * MHF_Chest
 * MHF_Melon
 * MHF_OakLog
 * MHF_Pumpkin
 * MHF_TNT
 * MHF_TNT2

Bonus:
 * MHF_ArrowUp
 * MHF_ArrowDown
 * MHF_ArrowLeft
 * MHF_ArrowRight
 * MHF_Exclamation
 * MHF_Question

Trivia

 * Heads are one of the few blocks that do not have their own textures and take their textures from other objects.
 * As such, when breaking any head, the particle effect of breaking it is the same as soul sand.
 * All heads are the same size (even though Wither Skeletons have larger heads than the other represented mobs).
 * Heads will break upon contact with water and lava.
 * In demo mode after the demo period has ended, breaking a Wither Skeleton skull will cause it to reappear as a normal skeleton skull.
 * Although mob heads do not protect the player, they can be enchanted and will apply enchantment effects to the player when worn.
 * Enchanted mob heads only have the purple "enchanted" texture over their inventory icon, and will appear to be unenchanted when worn or placed.
 * Heads will not cause cacti to break when placed next to them.
 * If in survival you break a player head with a custom skin, it will drop the head with the custom skin stored.
 * It will be named "Head" instead of " 's Head" though.
 * There are no horse, Guardian, Ender Dragon, Elder Guardian, or Wither heads in the MHF_(Mob) heads.