Fish

Barracuda in warm seas may announce themselves by snapping off a swimmer's toes. Giant carp bite for 2-20 and swallow anyone who takes 12 or more from one bite. Giant catfish bite for 3d4, gulping the target when the attack roll beats the needed number by 4, and a thrash of the head lets their toxic feelers lash up to two other nearby foes for 2d4 (1d4 with a save vs. poison).

In deep fresh water, giant gars bite for 8d4 and swallow on a 20, taking anything up to roughly 5 feet long, while camouflaged giant pike strike so fast that victims suffer -2 on surprise. A manta ray engulfs one man-sized or three small creatures if its roll beats the needed number by 2 or more; anyone attacking its rear meets a stinger for 2-20 and is stunned 2-8 rounds unless a save vs. paralyzation succeeds.

Piranhas run in schools of 5-50. Anything swimming or wading close has a 75% chance of drawing at least one bite, and once blood flows the whole school goes berserk, each fish biting twice a round and up to 20 swarming one man-sized target. Quippers are cold freshwater piranhas.

Dragonfish bite for 1-6, though most victims simply tread on them and take 1d6 spines through the boot, 1 point apiece, each snapping off in the flesh. Their slow venom kills unless a save vs. poison at -4 succeeds, and survivors fight at -2 for 1d12+4 hours. Stepping on a pungi ray is one spine attack that forces a save vs. poison or death; falling onto it means 2-8 such attacks, and if attacked it just swims off. A sting ray stepped on whips its tail spine, and the target is paralyzed for 5-20 turns on a failed save vs. poison.

An electric eel's jolt fills a 15-foot radius: 3d8 within 5 feet, 2d8 out to 10 and 1d8 beyond, then an hour of recharging. Marine eels shock the same area for 6d6, 4d6 and 2d6, and victims who fail a save vs. paralyzation are stunned one round per point of shock damage. Both ignore electricity. Giant eels have no shock but strike so quickly they gain +1 initiative.

A weed eel's poison bite kills in 1d4 rounds on a failed save vs. poison. Colonies live 25 to 40 feet down in fresh or salt water around a central cave roughly 30 by 20 feet and 20 feet high, its floor littered with scavenged coins, gems and pebbles. Six-foot tunnels lead out to a honeycomb of 6- to 8-inch burrows, one per eel, and the colony fights savagely to protect the central cave where its young grow.

A lamprey clamps on with its round sucking mouth and drinks, each round after the bite, 2 hit points for every Hit Die it has; sea lampreys save at -2 against fire. A land lamprey hits for 1 point, then drinks 1 point a round for three rounds, stopping sooner only if killed or pulled off, and each one clinging to a character hampers him like losing 1 point of Dexterity.

Sharks scent blood a mile away, and blood plus the thrill of killing drives them into a feeding frenzy. Since each darts in, bites and backs off, ten ordinary sharks can attack one man-sized victim at once. Giant sharks, the megalodons, never frenzy; an attack roll 4 better than needed lets them swallow most prey whole.

A giant sea horse head-butts. A trained mount can also wrap its long tail around either its own target or its rider's; the coil does no harm by itself but leaves the captive open to more butts, and escape takes an open doors roll at -1.