Java Edition 1.2.1

1.2.1 is an update which added a new height limit as a result of the anvil file format, zombie sieges and generated features including jungle biomes, wooden bridges in abandoned mineshafts, and desert wells. It also added new blocks/items - the bottle o' enchanting, redstone lamp, fire charge and chiseled stone bricks and new mobs - iron golems and ocelots.

Blocks

 * Chiseled Stone Bricks
 * Only available in creative mode
 * Redstone Lamp
 * Visually resembles Glowstone
 * Gives off light only when it is powered
 * Has a luminance of 15 when powered
 * Jungle Wood
 * New type of wood that spawns as jungle tree trunks
 * Has a slightly mossy brown texture with horizontal bark
 * Jungle Sapling
 * Can be grown into Jungle trees and drops from Jungle leaves
 * Jungle Leaves
 * Generates in Jungle trees and bushes
 * New textures (SandstoneGlyphs-Unused.png SandstoneFace-Unused.png)'''
 * Not in-game
 * Planned to be used as decorative sandstone variants

Items

 * Bottle o' Enchanting
 * Can be used to spawn experience orbs.
 * Only available in creative mode
 * Fire Charge
 * Produces fire when used
 * Can be fired from dispensers
 * Also a substitute for flint and steel

Mobs

 * Iron Golem
 * Occasinally spawns in Villages
 * Defends Villagers against Zombies and other hostile mobs
 * Can be spawned by placing 4 iron blocks and pumpkins in a specific pattern
 * Ocelot
 * Can be tamed using fish as cats
 * Cats will scare off creepers and teleport to the player similarly to tamed wolves

World generation

 * Jungle biome
 * A very dense, but rather uncommon biome featuring large jungle trees that can reach up to 31 blocks tall with 2×2 thick trunks. Oak trees are also common. Leaves cover much of the forest floor.
 * Desert wells
 * Rarely found in deserts
 * Abandoned mineshafts'''
 * Generated with wooden bridges in midair portions

Gameplay

 * Zombie Sieges
 * Will occur occasionally at night in NPC Villages

General

 * Warning Message
 * Worlds created prior to 1.2 will say the message, Must be converted!

Blocks

 * Dispenser
 * Changed texture
 * Grass
 * Placing blocks on grass will replace it
 * Ladders
 * Re-added collision box
 * Crafting recipe now yields 3 ladders instead of 2
 * Lava
 * Lava now has a faint rumbling sound effect, and large particles that hop out of the lava produce a popping sound
 * Oak Sapling
 * Changed texture
 * Slabs & Stairs
 * Can be placed upside-down by placing them below a block
 * Crafting recipe for slabs now yields 6 instead of 3
 * Vines
 * Can now be climbed like ladders

Mobs

 * Cave Spider
 * Swim extremely fast with the water stream towards the player, but seem to be almost not moving against the water stream
 * Creepers
 * Now stalk the player
 * Villager
 * Will breed if there are enough empty houses in a NPC Village
 * Wolf
 * Tamed wolves are able to breed using bones
 * Zombie
 * Can break down doors on Hard and Hardcore mode
 * Have a rare chance to drop an iron ingot, iron helmet, iron shovel, or iron sword
 * Rush to the nearest shadow or body of water for safety if it catches fire in daylight
 * Chase and attack villagers and doors (breaking them on Hard and Hardcore difficulties)
 * Sometimes zombies attacked villagers in preference to the player, and always chose the shortest way to the target, even if there was a door in the way
 * Skeleton
 * Have a rare chance to drop a bow or an enchanted bow
 * Rush to the nearest shadow or body of water for safety if it catches fire in daylight
 * Snow Golem
 * Will melt and die in the Nether
 * Will form a wall to attack mobs
 * Zombie Pigmen
 * Have a rare chance to drop a golden helmet, gold ingot, golden sword, or an enchanted golden sword
 * Swim fast in water

Gameplay

 * F3 debug screen
 * New Legends
 * lc: Largest section height
 * b: Shows what biome you are in
 * bl: Block brightness
 * sl: Sky brightness
 * rl: Raw brightness
 * Multiplayer
 * Due to biome data saving to chunks, SMP servers no longer send clients their world seed, displaying as "0" to the client
 * Third person view
 * Now has a slight delay on the speed at which the head moves on the player
 * Makes it possible to see the sides of the player's head

General

 * Anvil file format
 * New map file format
 * Increases the world height limit, from 128; to 256
 * World selection screen shows worlds saved in Region file format, and will convert them.
 * No longer shows worlds saved in Alpha level format.

Fixes
3 bugs fixed


 * Doors have been updated so that double-doors work better with redstone.
 * Ambience works in Multiplayer.
 * Mob spawners show the correct mob in SMP (instead of a pig).

Official Video
Similar to 1.1, a official video documenting some of the 1.2's major features was released on Mojang's official YouTube channel on March 1, 2012. The video was made by Hat Films, who have made update trailers and videos for Mojang in the past.

Further revisions

 * 1.2.2 fixed an issue with world generation.
 * 1.2.3 fixed some crashes that were present in 1.2.1 and 1.2.2.
 * 1.2.4 added new types of wooden planks, sandstone blocks, chat history, and a bunch of bug fixes.
 * 1.2.5 added "Pick Block" key, cats more eager to sit, and a handful of bug fixes.