Octo-Jelly

This deep-water octopus is shaped like a bell, with two swimming fins. Webbing joins its arms almost to the tips, so they look stubby and form a fleshy trap. It is effectively blind, sensing prey by touch and vibration, and though it can match the seabed's color instantly, in the dark that rarely matters.

Drifting like a jellyfish or creeping along the bottom, it settles over a victim and folds it inside the webbed bell. There the beak bites for 1d10 and the clammy flesh smothers for 1d6, both automatically each round until it breaks loose or dies. A trapped creature breaks out at the start of any round with a save vs. petrification at -1. Its body is so soft that every attack on it also deals full damage to anyone inside.

Fragile but nearly fearless, it retreats only after losing 75% of its hit points. Against a stronger enemy it can release a luminous blue-green cloud 20 feet high, 30 wide and 30 long; those inside are blinded for a full turn, lose initiative and defend at -2.

The depths cannot feed groups, so octo-jellies live alone, pairing only to mate. Young shelter briefly in the mother's bell before dispersing. They rarely surface unless some great undersea upheaval drives them up.

It eats any animal it can kill, and nearly all its neighbors eat it in turn. The soft skin has no commercial use, though the flesh is edible. Collected ink particles can go into the ink for light, continual light and the prismatic spells, and each creature yields enough to write a single spell.

Octo-hide: This huge relative, at least 20 feet across, has short webbed arms and crawls the deepest sea floors in ever-changing colors and hunts both swimmers and bottom dwellers. Each round it can breathe a cone of cold 30 feet long and 10 wide for 3d6 damage (half with a save vs. spell) to weaken prey, and cold of any kind cannot harm it. Its beak deals 2d6, and once the beak connects its arms close around the victim, ending the need for attack rolls. At 25% of its hit points it drops its prey and withdraws behind a blinding cloud like the octo-jelly's (lost initiative and -2 defense for a turn), but sized 40 feet high, 60 wide and 60 long. Octo-hides are solitary, mate briefly, leave their eggs immediately, and their ink is just as valuable for scrolls.