Jellyfish – Caught with a net or a butterfly net. Strike with lightning on melee attack. Needed to craft harpoons, gas masks, sea traps, and brain caps.
Seaweed – Reduces sanity when eaten raw. Can be roasted over a fire, dried in a drying rack, or cooked in a cauldron. Used to craft captain’s hats, antidotes, mussel sticks, and shell armor.
Brainy Sprout – Restores sanity when nearby. Once every three days, you can harvest brain matter from it to craft a brain cap or as food (+50 sanity, +10 hunger, -10 health).
Coral reef – Can be mined with a pickaxe to obtain coral used to craft antidotes and limestone.
Octopus King – If you give him a fish, he will pull a chest out of the water containing 1 doubloon and one random item. If you give him sea trash, the chest will contain 5 doubloons. You can only give items once a day.
Ship Horses – Guard the portal, throwing coconut shells at the player (not very accurate, but if they hit, they cause significant damage to the boat). They have 500 HP and are fairly easy to kill with a spear or saber. Each horse drops 3 gears. They appear randomly in the world, swimming to whales/coral reefs/coastal areas.