The pile of treasure shifts and slides away, revealing the form of an impossibly huge crab, its thick carapace studded with gold and gems. If the histories are accurate, a determined wizard decided to make himself an underwater army of gargantuan crabs to guard his island lair.

He succeeded in all but one respect. In granting the crabs the intelligence to understand and execute his orders, he accidentally made them both evil in outlook and far too intelligent to control. Communing with the sea in which they dwelt, the crabs taught one another to call forth the magics of nature itself and overthrew their creator, destroying his lair and scattering themselves throughout the sea. His later-discovered journals, history claims, reveal he originally created 3 dozen such crabs. Though they are unable to reproduce, rumor holds that nearly all have survived to this day, hidden in the deepest of underwater caverns, ruling the seas around them.

Dragon crabs tend to be greedy, both in carnivorous appetite and for treasure. Like some dragons, they often amass vast piles of gems, coins, and any other wealth that can survive at the bottom of the sea. Some also collect shipwrecks to decorate their lairs. Dragon crabs enjoy the pain of living creatures, especially intelligent ones, and often make a hobby of devising clever means to lure humanoids to their lairs to make them suffer for entertainment. Most dragon crabs harbor a strong dislike of wizards.

Though not universal, many dragon crabs line their shells with gaudy precious metals and stones, both for aesthetic reasons and to disguise themselves as piles of sunken treasure. Such crabs then bury themselves in loose sand and wait for unsuspecting adventurers to swim close and be ambushed. When not gem-encrusted, dragon crab shells are deep orange and grey, with patches of pale blue on the legs. They are about 60 feet in diameter, with pincers each as large as an elephant.