Mob Augments
Four augments come from organs dropped by vanilla ocean mobs.
Each organ is installed at the Augmentation Station as it drops, with no crafting.
Guardian Eye
Slot: Eyes. Drops from Guardians, about one kill in forty.
Hold L to fire a guardian beam at the first living thing along your line of sight, up to 15 blocks away. It stops at the first solid block, so you need a clear line to the target. Water does not stop it. Each hit deals 3 magic damage (configurable, guardianAugmentDamage), and it keeps firing for as long as you hold the key, with no cooldown and no power cost.
It shares the Eyes slot with Abyssal Eyes.
Dolphin Fin
Slot: Body. Drops from Dolphins, about one kill in five.
Gives you Dolphin's Grace II whenever your head is under water, so you swim much faster. It takes the Body slot, the same one as flight and Photophore Skin.
Drowned Lungs
Slot: Lungs. Drops from Drowned, about one kill in twenty.
Keeps your air bar full while you are under water, so you never drown. It is the only augment for the Lungs slot, so it never competes with anything.
Eldritch Heart
Slot: Heart. Drops from Elder Guardians: each one has roughly a three in five chance to drop at least one.
While you are in water it heals you half a heart every second.
You also need one to craft the Augmentation Station, so keep the first one for that. It shares the Heart slot with the Auxiliary Ventricle from Crafted Augments, which doubles your maximum health instead.