This guide is a simplified overview of all the changes in the Combat Update (Java Edition 1.9.x releases), which assumes at least some familiarity with the Bountiful Update (Java Edition 1.8.x releases).
The ender dragon can be respawned by placing one end crystal on each side of the exit portal at any one of the three blocks of that side.
While respawning, beams shoot out of these crystals, that will reset all the pillars and when done they blow up and spawn the dragon.
Subsequent dragons will spawn new gateways up to a total of 20, but won't create new dragon eggs and will only drop 500 experience instead of the usual 12,000.
When the dragon is respawned, the circle of pillars and the crystals reappear.
Explosion particles appear on the tops of the pillars as they are being rebuilt.
The fight has been changed to be more similar to the one on the console edition.
Doors are now placed facing left/right depending on which half of the block the player clicks on unless neighboring doors cause them to place a certain way.
Armor points count for less as the attack strength increases: each 2 done by the attack reduces the effective defense points by 1 (), but not below 20% of the armor points.
Boats are faster, and no longer will crash and break on the shore.
Using the left and right keys will now turn the boat.
Using the mouse will no longer turn the boat.
Using the mouse, the player can look fully 90 degrees to the left or the right, but not behind.
Holding the sprint keys no longer have any effect.
Boats now sink when there's water above it, instead of floating upwards.
The player cannot use or attack while the boat is in motion.
Mobs and armor stands can go into boats, with a maximum of two.
Riding a boat no longer subjects water-sensitive mobs to being damaged by water, and no longer protects sunlight-sensitive mobs from being damaged by sunlight.
Luck of the Sea and the Luck effect affect fishing again, and effects stack. Each point increases the weight of treasure by 2, decreases the weight of fish by 1, and decreases the weight of junk by 2.
When an item with the enchantment is held or equipped (in the main hand, offhand, or armor slots), collected experience orbs repair the item at a rate of 2 durabilities per XP instead of adding the XP to the player's total experience.
If moving on ground (not falling, jumping, or flying), any still water blocks with air above within a radius of 2 + level around the block being moved to will be turned into frosted ice.
Frosted ices cannot be obtained in normal.
Frosted ices naturally melt fairly quickly with light and show the breaking texture.
Each Sharpness level now adds 1 damage to the base damage at level I and an additional 0.5 ( × 0.25) for each additional level, down from a flat 1.25 ( × 0.625) per level.