Minecraft wiki entry for Combat_Update, associated text: A method of restarting the ender dragon boss fight.
The infinite generating outer islands of the End, populated by chorus trees, end city structures and ships, and shulker mob.
"Off-hand" slot for dual wielding.
Attack cooldown mechanic.
Massively nerfed armor strength.
Attribute system expanded.
Shield, spectral arrow, 14 types of tipped arrow and a lingering potion for each type of potion.
Elytra for Gliding.
Subtitles.
Dominant hand option.
Igloo structures that generate in cold biomes.
Skeleton trap horses that spawn during thunderstorms.
13 new blocks: grass path, frosted ice, 2 new types of command block, chorus flower and chorus plant, end gateway block, end rod, end stone brick, purpur block, pillar, slab and stairs.
New items: beetroot with seeds and soup, end crystal, normal and popped chorus fruit, luck potion and dragon's breath.
5 new splashes.
4 new particles:
sweepAttack, dragonBreath, endRod and damageIndicator
4 new status effects:
Levitation, Glowing, Luck and Bad Luck.
2 new enchantments:
Frost Walker and Mending
5 new statistics:
sleepInBed, sneakTime, pickup, drop and aviateOneCm
Lots of new NBT tags.
3 new gamerules.
disableElytraMovementCheck, spectatorsGenerateChunks, spawnRadius
150+ new sound events.
Support for Chinese, Japanese and Korean, and probably other IME languages.