Pokemon lifespans rarely line up entirely with those of their trainers, and tragedy can lead even relatively short-lived species to survive them by many years. Conversely, trainers must often bury their pokemon, whether from old age or fatal injury. Both of these situations are held, in popular lore, to lead to the creation of Houndstone, with different stories popular in different parts of Paldea; folklorists are not sure which, if either, represents their true origin.
Although Greavard are extremely dangerous, Houndstone are not considered aggressive by the standards of ghost pokemon; they have accumulated plenty of life energy before evolving, and the duties of a watchdog do not require them to consume it very much at all. Indeed, their long afterlives spent watching over tombs have given rise to a very different type of ghost story; some say that Zacian's sword was once sheathed within a Houndstone, while others hold these pokemon, much like Cofagrigus, to be living graves, their masters buried under the stone on their heads.
Few modern people are desperate enough to rob a grave protected by a Houndstone, yet Paldean historians report many incidents of individuals who tried, and came to rest eternally in the same cemeteries where they sought treasure. The mausoleum of Paldea's first kings, unlike those of their contemporaries, has survived intact from antiquity, all through the Paldean Dark Age and the fall of the four ancient treasures. The few objects from those tombs currently displayed in the region's history museum were obtained only after protracted negotiations with some very old canine pokemon.