New things to do with Prismarine! Also, a new biome, the Devoid Sea!
The Devoid Sea features special Driftwood trees and both types of Guardians, you might even find a stray wolf!
How to craft everything: (Spoilers if you want to figure out on your own)
Aquaskin - Smelt Prismarine Crystals
Prismarine-Coated Egg - Put an Egg in the middle and put Aquaskin all around it
Aquatic Armor - Put Aquaskin in typical armor fashion
Spike - On the bottom middle put a Stick, then above it a Prismarine Shard, then above it a Gold Ingot
Spike Sword - On the bottom middle put a Stick then above it a Spike
Driftwood Plank - Put Driftwood in the middle of your crafting table