Origin Information:
Red Skinned: You're red like a Crab or Just really sunburned who knows...
Underwater Vision: You can see underwater.
Claw Damage: Your Claws allow you to do more fist damage.
Faster Swimmer: You Move Faster in your Natural Habitat.
Underwater Breathing: You can breath underwater.
Origin Negatives:
Lower Health: As you're a crab you have less health.
Fish Diet: You can only eat Fish.
Installation:
Place "crab-origin-1-18-1-18-2.zip" into .minecraft/saves/yourworldname/datapacks/
Server Installation:
Place "crab-origin-1-18-1-18-2.zip" into MinecraftServer/World/datapacks/