hey, i sometimes keep my promises.
Obviously, I seriously overestimated the CR.
Verme
Gargantuan Beast (Aquatic)
Hit Dice: 18d10+144 (243 hp)
Initiative: -1 (Dex)
Speed: Swim 50 ft
AC: 15 (-4 size, -1 Dex, +10 natural)
Attacks: Bite +23 melee
Damage: Bite 3d8+21
Face/Reach: 20 ft by 40 ft/10 ft
Special Attacks: Swallow whole
Special Qualities: Resist edge weapons, fire resistance 20, armored head
Saves: Fort +19 Ref +10 Will +6
Abilities: Str 39 Dex 9 Con 27 Int 2 Wis 10 Cha 6
Skills: Listen +10, Spot +10, Swim +15
Feats:
Climate: Any aquatic
Organization: Solitary
Challenge Rating: 19
Treasure: Standard
Alignment: Always neutral
Advancement: 19-36 HD (Gargantuan); 37-54 (Colossal)
The verme is probably the largest of all fish, able to swallow a large shark or even a baby whale in one gulp. These fish prefer great rivers, but are occasionally known to venture out into saltwater oceans. It can swallow creatures in the water, and can also eat things on the riverbanks, reaching its enormous armored head out of the water to snatch cattle or even humans. Its stomach is likely to contain metallic and other indigestible items, remnants of previously swallowed victims.
A verme resembles a catfish of unbelievable size, between 50 to 80 feet in length, with very large scales, and a mouthful of needles for teeth. Its underside is pale yellow, and its flanks run from dark brown to a mottling of green and brown along the back. This gigantically long fish is flat along the belly, and wider than it is high, to help it lurk along the bottom in shallow waters.
COMBAT
A hungry verme is a ravenous predator that will not be denied. It swallows any prey it hits, and is able to capsize even large craft. It will attempt to swallow creatures attacking its head before it attacks those on its sides. The fire resistance of the fish applies only to its outer body; fire affects the beast normally inside of the mouth or internally.
Swallow Whole (Ex): A verme automatically swallows an opponent of Large or smaller size by making a successful bite attack. Once inside, the opponent takes 3d8+4 crushing damage plus 2d8+4 points of acid damage per round from the verme's digestive juices. A swallowed creature can cut its way out by dealing 30 points of damage to the verme's digestive tract (AC 10).
The verme's gullet can hold four Large, eight Medium-size, or sixteen Small or smaller creatures.
Resist Edged Weapons (Ex): A verme's thick, slimy scales make slashing and piercing weapons nearly useless against it. Attacks from such weapons inflict only 1 point of damage, plus magic and strength bonuses.
Armored Head (Ex): The verme's bony head provides it with a +2 bonus to its natural armor class against anyone attacking its head. Any creatures subject to the verme's bite attack are considered to be facing its head in that round.
Originally found in Monster Manual II (1983), Monstrous Compendium Annual Two (1995) under "fish".