Better even than the Alaskan Bull Worm, Gary the Snail made his appearance in the waters off the Isle of Dread. He has the stats of a roper but with a big spiral shell.
The party was cruising along on its way to Scorpion Island when the ship's wheel gave a jerk accompanied by a wood crunching noise from the back of the ship. Gary was mostly submerged, trying to disable the ship's rudder. Only his eye-stalks poked out above water.
I assumed it was 40 feet from the rear of the ship to the water, so whoever looked down was within range of all six strand attacks. He pulled two characters off the deck before they started jumping down to him.
2d8 strength damage is a bugger when you're trying to swim in armor. Spell resistance 30 keeps the spell casters from ruining a good water fight.
The party ended up killing Gary, but now they're paranoid about evil, intelligent mollusks.