Java Edition 15w34a

15w34a is the tenth snapshot released for 1.9.

Additions

 * NBT tags
 * Added the  and   byte tags to   tile entity for command blocks.
 * Added the  (Integer) and   (List/Double) tags to.
 * Added the  string tag inside   for the   tile entity.
 * Added the  byte tag to   tile entity for note blocks.

Changes

 * Combat
 * New attack speed combat mechanic.
 * A meter shows up after switching items or attacking.
 * Damage done depends on the fullness of the meter.
 * Fills in 0.25s for non-weapons, 0.8s for swords, pickaxes, and shovels, and 1.2s for axes.
 * The meter can be displayed next to the hotbar (left or right based on the player's main hand), under the crosshair or turned off.
 * Looks like the icon for the effect on the side of the hotbar, or like a dagger under the crosshair.
 * This is controlled in video settings.
 * Delay when selecting a sword, pickaxe, axe or shovel into the main hand.
 * Maps
 * Now start at a wider zoom level (1:4 instead of 1:1).
 * New recipe for zooming in on a map: Shears and a map together in any shape.
 * Zooms in on the lower-right quadrant of the original map.
 * This causes the shears to lose durability.
 * Command blocks
 * New textures that now vary depending on what direction they are placed from, similar to dispensers and pistons.
 * It consists of a front, a back and a side texture (looks like arrows), so the orientation can be easily determined.
 * The texture is animated - the colored "buttons" in the middle change color.
 * The middle panel texture has a black outline.
 * 3 modes: impulse, chain, and repeat - color changes based on mode.
 * Impulse mode (orange): Command is run once on rising edge.
 * Same behavior and color as previous versions.
 * Chain mode (green): Command is run whenever another command block pointing into it executes, and the command block in question is powered.
 * The chain signal is forwarded until the blocks get out of loaded chunks.
 * The signal is independent of the powered state of any block in the chain, as well as the command (or lack thereof) inside.
 * Repeat mode (blue): Command is run every game tick while powered.
 * Like a minecart with command block but faster.
 * Each new mode has its own block id and is obtainable with and.
 * Power received is now a data tag, allowing command blocks to have such a state under control, independent of any nearby redstone signal.
 * Command block contraptions from earlier versions will still work.
 * The "Done" button is now always available to press, even when the command line is empty.
 * Minecarts with command blocks
 * The "Done" button is now always available to press, even when the command line is empty.
 * Note blocks
 * Their power state is controlled through a tag, and can, therefore, be controlled independently on any redstone signal.
 * Zombies and zombie pigmen
 * Now lift their arms slightly when becoming hostile.
 * NBT tags
 * for the  block entity has been deprecated.
 * Optimizations
 * Optimized mob AI, pathfinding and block ticking.
 * 15% tick speed increase on 16 render distance.

Video
Video made by slicedlime: