Environment any underground
Organization solitary
Treasure none or incidental

Delvers are enormous gastropods covered with corrosive slime and designed for burrowing through stone. Fifteen feet long and weighing several tons, they are most commonly encountered deep below ground, particularly near underground water sources. Surprisingly intelligent, these juggernauts exist to tunnel, surviving off metals— which they find intoxicating, and sometimes maddening— and leaving behind smooth, 10-foot-diameter passages.

To surface-dwellers, stone and earth are often the essence of safety and stability, their unchanging nature used as a metaphor for the stolid and the sensible. Yet below civilization’s very feet, strange creatures lurk in the darkness, twisting and reshaping the world to their alien specifications. With eldritch powers beyond imagining, these presences carve cavernous kingdoms for themselves, raising new races to sentience in their blind world of silent stone.

The all-powerful and mysterious master race that created the monstrous creatures called “delvers” by humans has long since departed, leaving the delvers behind as a living legacy. Cave slugs forcibly evolved into engines of construction designed to hollow out new realms for their lords, the delvers now follow their own mystical obsessions, burrowing through the earth with incredible power and speed and leaving a warren of tunnels in their wake. Though delvers possess no magic, their flesh is corrosive to nearly every material that humanoids possess. Also commanding a fierce intelligence and the strength to crush boulders to dust, delvers are slow to anger but terrible when riled.

Though delvers are not particularly malicious, they sometimes come into conflict with other races over their pressing desire to consume metallic ore. Once worked, metals hold less appeal for delvers, but when consumed in their natural state, different ores create a variety of powerful, intoxicating effects much sought after by the delvers. Even trace amounts of ore are enough to produce an effect when consumed in sufficient quantity, giving rise to the popular perception that delvers eat stone indiscriminately. This gluttony is the primary reason why most miners take a dim view of the strange slug-beasts, as few can stand and fight against the rage of a gorging, intoxicated delver feeding on an ore vein.

Still, so long as a significant distance is kept, the sight of a delver is not necessarily cause for alarm, as the creatures have little interest in attacking others save out of self-defense. Some canny adventurers have even made temporary alliances with the intelligent beasts, offering vast amounts of raw minerals and metals in exchange for guidance or service, whether it be directions to a specific site (for delvers see much in their wanderings) or even a custom-built tunnel to reach it.

Ecology

The first delvers were created by an unknown race for two reasons: to hollow out magnificent subterranean chambers and tunnels for their masters and the other servants, and to disarm or destroy any creatures who dared stand in their way.

To those ends, the delvers’ creators wrought exceedingly well. Taking inspiration from the body of a cave slug, they created a supple creature covered in a highly acidic mucus that could dissolve rock and adapt quickly to new kinds of materials. This protein slime from the delver’s rocky skin also acts as active camouflage, so that the rare delver who’s over-matched by an enemy or lying in wait for an intruder can withdraw into a hastily dug hideout and remain unseen. Water can wash the slime away; otherwise, it continues to burn after the initial touch, horribly corroding and blistering whatever it clings to. If a delver is attacked, its slime protects the creature by dissolving its attacker’s weaponry. Only those immune to acid can consider themselves safe from the delver’s slime, and even they must still contend with the delver’s powerful pseudopods. While the delver can move without the aid of its pseudopods, these long tendrils are also coated in acidic ooze and assist in scraping rock down from the walls, enlarging tunnels and caverns and shaping them with remarkable dexterity. In combat, these appendages also act as fearsome bludgeons of tremendous strength.

The delver’s body is largely compressible. Although it cannot stretch a great distance, it can compress its enormous bulk into a very small space, granting it the ability to seep through cracks and holes only 5 feet wide. This allows the delver to enter small spaces and enlarge them from within, as well as to survive the crushing weight of rocks dislodged by its passing. The delver has no skeleton, and instead maintains its shape through the gaseous by-products of the chemical stew that constantly churns throughout its body. The delver can also choose to exude a lesser form of acid from its tentacle-like pseudopods that merely softens stone rather than destroying it, assisting the delver in creating chambers of specific shapes and sizes.

The delver subsists entirely on the metals, minerals, and microscopic organisms that it sloughs off stone with its acid, turning solid rock into a slurry that it then absorbs through its mouths, which take up much of its underside. Hundreds of rings of tiny cilia underneath the delver aid it in movement, anchor it to the tunnel floor it creates, and sweep minerals into its ever-hungry series of orif ices. The delver’s mouths are a series of small pores that absorb the granules into its body, where its stomach begins the process of converting the slurry into the mucus that dissolves the rock around it. The minerals it eats alter the appearance of both its slime and its flesh, and thus the delver often changes color to match its habitat within a few hours of burrowing through a new location.

Delvers wander according to their own indecipherable logic, but visit water sources regularly, as they require liquid to maintain the viscosity of their slime. If they do not refresh themselves within a month of their last immersion in water, they lose their protective coating. Any water-based liquid will suffice to renew them for a month’s time, though their presence fouls the water for some time afterward. Stories have emerged of fallen cities with delver-sized holes in the city’s baths, marking the place where the creatures emerged for a brief time. In some accounts, the city residents unwisely attempted to resist, resulting in a city crumbled into pits and canyons, inhabited by only a few mad hermits, and cave-dwelling wildlife nesting in the darkened holes of the cliff walls.

Delvers are extremely attuned to vibrations in the ground, and they can pinpoint the location of creatures moving through or across rock and earth anywhere within 60 feet, regardless of how many feet of solid rock might separate them. Their special sensory prowess also allows them to find fault lines and hair-thin cracks in the stone.

Delvers reproduce asexually, depositing five to 10 eggs on the shores of an underground river and then departing; they can repeat this process up to three times over the course of their 300-year lives. They do not hold any parental feelings or duties toward their young, nor do they protect them. As a result, delver eggs and young are highly prized by those knowledgeable about such things; if caught within the first few weeks, the impressionable young creatures can be raised and trained for a variety of roles, though most eventually shake off their training and abandon their masters to roam the deeps in answer to some unconscious and instinctual draw.

Delvers can travel miles deep within the crust, and even their undisturbed wanderings can prove hazardous to nearby races. In the past, delvers have broken through into magma-filled chambers deep beneath the surface, opening old lava tubes and awakening dormant volcanoes. Others permanently weaken the bedrock of mountains, trigger avalanches onto alpine towns, and even foster earthquakes in areas already prone to such shocks. While all of these are generally presumed to be accidental byproducts of the delvers’ wandering, some whisper that such disturbances are in fact deliberate, the result of evil machinations by either the delvers or some hidden hand that guides them.

All delvers love metal, and in general the purer the deposit of ore, the better its taste. Part of this attraction is due to the flavor of the stuff, but an even greater part revolves around the fact that metal acts as an intoxicant to delvers, like fine wine or a pleasurable drug. Delvers love copper, silver, and gold, but prefer iron most of all, with a heavy vein sending them into a debauched rapture that perhaps only rust monsters or xorns can truly understand. Though delvers frequently look down their proverbial noses at worked metal—the heating and tempering cause it to grow stale—most aren’t above sneaking a bite of such things when they’re proffered... or even when they’re not. More than one adventurer has met his end when a starved delver, kept away from metal and driven mad by lust for it, has devoured the humanoid’s metal armor without worrying about the messy fate of the humanoid inside it.

Even worse than the addicts are the rare delver warbeasts, juggernauts capable of burrowing through any defenses and sending warriors flying with deadly, corrosive whips of their pseudopods. Some such creatures are the result of manipulation and mind control by powerful spellcasters, or years of training by the cruel masters of subterranean menageries. Others are the result of a specific mixture of metals and minerals so potent as to drive the delvers insane with rage and lust, either administered intentionally by others or accidentally ingested in the course of a delver’s normal grazing. Some guess that a few of these may even be of a different breed altogether, a sect of delver society created by their long-lost progenitors with the specific goal of defending their realm and purging the surface world of undesirables. Whatever the case, the result is the same: devastated towns and cities, fleeing spelunkers, and terrorized mountaineers. When their minds have been set in this mode, delvers become ruthless and unresponsive. Even the offer of metal is unlikely to elicit mercy; more often, they simply take what they want and move on. This combat fugue can last for hours, months, or years, and for most civilized races confronted with an enraged delver, the best recourse is flight—a desperate, headlong race for safety. For when a delver has its mind set on destruction, little can stand in its way.

Habitat & Society

Delvers are by their natures solitary creatures, rarely interacting with others of their kind. As the primary pursuits of delvers are the creation of new tunnels and the discovery of rare metals to devour, an abundance of the creatures means a rapid weakening of the rock around them and a quick exhaustion of whatever ore the stone has to offer. Recognizing this, delvers tend to distribute themselves far and wide, and may even clash over rights to a given territory (though most delvers are far too reasonable to attack their own kind unless in the throes of ore-lust).

While exceptionally intelligent, even by the standards of human sages and arcanists, delvers have goals that prove incomprehensible to most humanoids. For while humans generally presume that it’s the delver’s hunger for metal that drives them, only those who carefully study the great creatures understand that the intoxication provided by the metals is not sought merely for its pleasant effects, but also as an important component in the religious rites around which delvers’ lives revolve.

Every delver is, at heart, a mystic with a deeply ingrained racial memory and desire. After their abandonment by their alien progenitors in the dim mists of prehistory, the delvers were left with a slowly developing sentience, but no sense of purpose—building machines without a blueprint. Over time, they came to believe that their abandonment was a test created by their former masters, and they devoted themselves completely to fulfilling their obvious destiny as the greatest builders and architects the subterranean world had ever seen. Some pursue this mastery out of rage, desperate to show up their arrogant creators. Others do so out of a belief that, when they’ve finally perfected their art, their masters will return to lift them up to yet another plane of existence. Regardless of their differences in faith, all delvers work toward a single goal: turning the stone and earth of their world into a single, interconnected palace of tunnels and caverns.

In the same way that some shamanistic humanoid tribes use sacred drugs to aid in vision quests, delvers allow themselves to become intoxicated by metals in order to open their minds to the plan of the ancients. This pursuit of aesthetic perfection also helps explain why delvers don’t build themselves great cities or organize in a more traditional society. To them, the world itself is their city, with tunnels its streets and caverns its palaces, and further organization is counterproductive when each delver can best pursue its destiny by wandering alone and listening for whispers of the creators’ hidden plan.

Delvers are generally indifferent to others of their kind, and they rarely attack each other unless they are maddened by an overindulgence of metals (in which case the sober delvers attempt to avoid the enraged member while it’s “in the grip of the masters”). They do not mind the incursion of humanoids—whether good or evil—into their tunnels, provided the infiltrators’ use does not significantly alter the tunnels’ layout. Upon occasion, a more sociable delver has been known to converse with other creatures, especially if it believes they may have something to offer it (such as a specif ic metal or mineral that it’s unable to forage for itself or take by force, or potential information about their lost masters). If the reward is great enough, delvers may agree to serve an underground city of pechs, svirfneblin, or similar creatures for a time, cutting defenses in the stone and aiding the creatures during raids on nearby enemies—though the latter usually requires the petitioners to explain how this furthers the delvers’ interest in carving the world’s stone to their own specifications. Most dwarves, duergar, and other mining creatures find delvers to be a terrible threat to both their homes and their industry, and either attack or avoid them accordingly.

Campaign Role

Though they only rarely emerge above the surface, seeing the world of light and air as completely without interest or application to their tunnel-digging mandate, delvers are a danger well known to those races and adventurers that spend significant time underground. PCs in the know might recognize delver territory by the perfectly formed tunnels crisscrossing one another at apparently random points, and they might either avoid the area for fear of upsetting its powerful residents, or else use the network of tunnels as a convenient highway through the subterranean deeps.

Delvers can play numerous roles within a campaign. Some might be simple adversaries, metal-maddened monsters that attack the PCs in a blind rage or smash their way into a strategically important mine or subterranean holding. Perhaps a given delver has taken issue with the humanoids who have inhabited and expanded a particular tunnel complex (thus destroying the artistic perfection of the delver’s existing tunnels), or simply sees a dwarven fortress as an obstacle to be burrowed through and reworked into a proper delver creation. A delver might be responsible for vast natural disasters, such as terrifying urban sinkholes or the draining of a key reservoir into subterranean tunnels. A delver could even be a prophetic herald of its long-forgotten masters, preaching of their imminent return to retake all the kingdoms beneath the earth.

At the same time, delvers can be valuable resources. An adventuring party might be forced to bargain with a delver in order to gain access to its tunnels, or to learn the location of a hidden, subterranean hoard or realm visited by the delver during its long history. On rare occasions, a delver might even be persuaded to help create fortifications or defend a location, and a delver subjected to mind control makes a nearly unstoppable siege-breaker. Of course, most delvers retain a high opinion of themselves (and a comparatively low opinion of others), so anyone seeking to bargain for such services may have to work quite hard to find something the delver values more than time spent digging its tunnels. And while intimidation and mind-control are both viable options, a character who attempts such an action and fails may find himself needing to avoid subterranean environs for the rest of his life, lest the delvers catch up with him and punish him for his presumption.

Treasure

Delvers do not typically collect treasure, and their vagrant lifestyle usually leads them to abandon all possessions that can’t be easily worn or carried with them (with exceptions being items such as ioun stones, which follow along of their own accord). Typical delvers would much rather have knowledge, especially information related to architecture or the nature of their departed masters, than any physical object.