In Hari Ragat, one of my design guidelines for creating creatures is that if it’s too big to be natural it’s supernatural; that is, it’s likely to have some special abilities beyond being a super-sized version of whatever animal it’s based on.
Tambanokawa, or Elder Cave Crab
This Elder Crab inhabits a sea cave on any island of your choice and is the size of an elephant. It is thousands of years old, which has given it not only time to grow in size but also in spiritual power. It will defend its territory from intruding boats, will happily take divers and fishermen for breakfast, and sometimes comes up to land to hunt. Now it has discovered your village.
When Tambanokawa hunt on land they summon a heavy rain to cover their approach; this keeps their gills wet, drives prey to cover where they're easier to find and corner, and gives them advantage in combat. In combat they use their two differently-sized claws in deadly combination: the large claw is often used to hammer prey down first, the faster small claw is then used to seize the prey, the large claw grabs and holds fast making escape impossible, then finally the small claw starts tearing off chunks of flesh to put in the crab's mouth.
If it can grab an opponent thus, it starts to feed while its vicitim is still alive, even if it has to continue fighting while eating. Assume the Tambanokawa hits with its big claw on an even, and with its small claw on an odd roll.
If it loses both eyestalks in battle it retreats immediately back into the sea. Any eyestalks, claws or legs it loses in battle will regenerate within a year while it hides in its cave, and then it comes back. It can only regenerate however in its own cave.
Tambanokawa 6/24, Impenetrable Carapace, Monstrous Scale Right Claw, Summoner of Monsoon Rains, Retreats if Blinded, Regenerates Lost Eyestalks and Limbs After a Year, Renown Value 30