The ancient Numenorean sorcerers tinkered with life forms on occasion leaving as their only record ancient scrolls.
The kelpkraken consisted of a good dozen sea weed tentacles, each about 20' long, surrounding a core of stinking, compressed plant fiber that passed for a mouth and gullet. It tended to collect objects that could serve as a form of makeshift camouflage, and half its tentacles would, at any time, be decorated with old helms, human skulls, and various pots and other containers it had picked up off the bottom of the sea.
When the kraken was awake, the scent of blood would stir the monster into seeking warm food most of the time. It could not abide light and always attacked in the dark. It was fairly stupid and would only locate the exact source of the blood less than half of the time. Anyone seeing the kraken for the first time was in danger to be stricken and stunned with terror. The kraken itself had a chance of withdrawing in a panic every time a reasonably bright light shined on it. Even if the kraken was not severely injured, it would sicken from its exposure to the surface air and withdraw to the bottom of it's bay home after I -5 days.