You don’t have to move (or breathe air) to be deadly.
Sailors swept overboard in a gale are pulled by the current into a cluster of giant sea anemones. (The sailors are treated as bull-rushing…but of course, the anchored anemones are resistant to such conditions.)
Cecaelias raise constricting darkforest anemones to guard their oyster beds. The octopus-folk cover themselves in a pungent slime (produced by pet giant clownfish) when they go to harvest the mollusks for meat and pearls.
A deep tiger anemone does not hide a sunken treasure, but rather a sunken mystery: a pyramid of unknown origin studded with gems and carvings. The object radiates both abjuration magic and an aggressively neutral divine aura, discomfiting the few sages who could survive both the crushing water pressure and the anemone’s acid attack.
—Pathfinder Bestiary 3 238