Zombified Piglin

Zombie pigmen are common neutral mobs that live in the Nether.

Spawning
Zombie pigmen can spawn in the Nether, from Nether portals, or from pigs. They have a 5% chance of spawning as a baby zombie pigman, and a baby zombie pigman has a 5% chance of spawning as a pigman jockey.

All zombie pigmen spawn with a golden sword, which may randomly be enchanted. This chance increases at higher difficulties, and the sword's enchantment will more commonly be of a higher level.

Nether
Zombie pigmen spawn in groups of 4 in the Nether at any light level.

Nether portals
When a Nether portal block in the Overworld receives a block tick, there is a small chance (1/2000 on Easy, 2/2000 on Normal, and 3/2000 on Hard) it will spawn a zombie pigman on the portal frame beneath it. If a zombie pigman spawned in this way does not leave the portal it spawns on, it will never be teleported to the Nether.

Pigs
A zombie pigman will spawn when lightning strikes within 4 blocks of a pig. If the player is riding the pig when lightning hits it, a zombie pigman will appear on top of the player. Even if the pig is a baby, the zombie pigman will still be full sized.

Drops
Zombie pigmen drop 0 to 1 rotten flesh and 0 to 1 gold nuggets. The maximum amount of each can be increased by 1 per level of Looting used, up to a maximum of 4 each at Looting III.

Zombie pigmen have a 2.5% chance to drop a gold ingot and a 8.5% chance to drop their sword when killed by a player or tamed wolf. That chances of each can be increased by 1% per level of Looting used, up to a 5.5% chance for a gold ingot and a 11.5% chance for a golden sword at Looting III.

Zombie pigmen drop 5 experience, or 12 if they are a baby zombie pigman, when killed by a player or tamed wolf. Since 1.8, deaths of hostile pigmen will always be registered as kills by the player they are targeting, regardless of whether that player ever touched that pigman.

All items zombie pigmen have picked up after spawning will be dropped upon death.

Halloween
On Halloween (October 31), zombie pigmen have a 22.5% chance of spawning with a pumpkin or a 2.5% chance of spawning with a jack o'lantern equipped as headgear.

If a zombie pigman wearing a pumpkin or jack o'lantern is killed using a tool enchanted with Looting, there will be a chance equivalent to the level of Looting used to drop the pumpkin or jack o'lantern, up to a maximum of a 3% chance at Looting III.

Behavior
Zombie pigmen tend to move relatively slowly. They can drown, but are immune to fire and lava damage. Baby zombie pigmen are faster than adult zombie pigmen.

Like zombies, some zombie pigmen will sometimes bang on wooden doors, and in Hard difficulty, they even break them.

Some zombie pigmen have the ability to pick up items. They will even pick up a weapon if they feel it is better than their golden sword, dropping their golden sword with the same chance as if killed with Looting I.

Combat
Zombie pigmen have health and  armor points, which reduces about 8% of damage.

When aggravated, their speed will significantly increase to faster than the player's walking speed. They will also make an aggressive noise between 0 to 39 ticks after they are attacked. The pigmen will crowd around and try to overwhelm the player by ganging up on them. Each pigman can deal on Easy,  on Normal, or  on Hard per hit.

In addition, some zombie pigmen will have the ability to spawn reinforcements when attacked, including when killed in a single hit. Due to a bug, the spawned reinforcement will sometimes be a regular zombie.

Zombie pigmen are damaged by the status effect Healing and healed by the status effect Harming. They are immune to both the status effects Regeneration and Poison.

Hostility
Zombie pigmen are not initially hostile, but all zombie pigmen within a 67×67×21 to 111×111×21 area centered on the attacked pigman will become aggressive and converge on the player if any individual is attacked, unless the pigman attacked is killed in one hit. This applies to any hit registered as coming from the player or other mobs, including deflecting ghast fireballs.

Zombie pigmen will remain hostile for 20 to 39.95 seconds, although they will continue to pursue an already-targeted player after this time until the player escapes their 40 block pursuit radius. Approaching within 35 blocks of an already hostile zombie pigman causes it to sound an alarm call, angering other zombie pigman in a 40-block radius. The forgiveness timer does not advance for zombie pigmen in unloaded chunks. Thus, if the player enters a Nether portal and returns, any provoked zombie pigmen in the area will still be aggressive unless another player was nearby to keep the chunks loaded. Dying will not cause zombie pigmen to become neutral towards the player, regardless of whether they killed you. Furthermore, they will still pursue even if the player is under the effects of Invisibility.

Data values
Zombie pigmen have entity data associated with them that contain various properties of the mob. Their entity ID is.

Trivia

 * The zombie pigman skin file has "THX XAPHOBIA" written on the unused section as a credit by Notch to the skin's original creator, XaPhobia.