Your vision will gradually increase the longer you're underwater
Overhauled world generation
Overhauled command parser
Added new world type "Buffet"
Allows you to create worlds with a unique biome
More features will come to the Buffet world type in later updates
Added a bunch of new sounds
Added three new pieces of music
Added underwater ambience sounds
Added a swimming animation
Press your sprint key underwater to start swimming
Added data packs
Allows you to edit recipes, tags, loot tables, functions, and advancements
Added new advancements
Some blocks can now be waterlogged
Use a water bucket on a block to surround it with water
Added an "Optimize World" button (singleplayer -> edit world -> optimize world), which upgrades an entire world from older version to the latest version in one go
Blocks
Added blue ice
Found in icebergs
Added coral blocks
Added coral fans
Added coral
Added conduit
Combine 1 heart of the sea together with 8 nautilus shells to create the conduit
Makes your life underwater a lot easier
Added dried kelp block
Combine 9 dried kelp to create a kelp block
Added kelp and seagrass
Normal pumpkins no longer have a face
Added carved pumpkin
Use a shear on a pumpkin to carve it
Added sea pickles
Added bubble columns
Use either magma blocks or soul sand to create a bubble column
Added wood block
Combine 4 logs of any type to create a wood block
Added stripped wood
Right click with an axe on either logs or wood to create stripped wood
Added prismarine stairs and slabs
Added variantes for all 6 types of woods for pressure plates, trapdoors and buttons
Added turtle eggs
Be sure to protect them from hostile mobs
Mobs
Added tropical fish
Added turtles
A friendly mob that lays eggs on beaches
Added dolphins
A neutral mob that will lead you to treasure if you feed it fish
Make sure to not hit them unless you want an entire pod after you
Added the Drowned
Hostile mob that can be found naturally in oceans and rivers
Can spawn with tridents
Zombies will convert into Drowned if they're underwater for too long
Added Phantoms
Get a good nights sleep if you don't want these coming swooping at you
Drops phantom membrane
Added cod, salmon, and pufferfish as mobs
Changed the horse model to be more consistent with other mobs
Removed Herobrine
Items
Added tridents
The newest weapon in Minecraft
Drops from the Drowned
Works as both a melee and a ranged weapon
Added trident enchantments
Added the ability to catch fish with buckets
Added map markers
Hold a map in your hand and right click on a banner to create a marker
Added heart of the sea
Found in buried treasure
Added nautilus shells
Drops from Drowned and can be found from fishing
Added phantom membrane
Dropped by Phantoms and gives you the ability to repair elytra and used for Potion of Slow Falling