Divine Characteristics

The gods of Theros are far more active than the deities of most D&D worlds. But that doesn't mean they are ordinary creatures - they aren't mere mortals, nor are they monsters that can be fought.

Further, the gods of Theros aren't omnipotent. Although they are physically and magically powerful, ageless, and all but indestructible, their actions are bound by the decrees of Klothys. They can tangle the threads of destiny to a point, but they are forbidden from overstepping their assigned places in the pantheon.
The god Kruphix is able to confine them to Nyx, preventing any direct interaction between the gods and the mortal world.

Likewise, the gods aren't omniscient, though they see and hear everything that occurs inside their temples and before their altars. They have perfect recall of everything they experience. Certain liminal spaces - cave mouths, shorelines, crossroads, forest edges, and so on - enable mortal voices to reach the gods as well, though most gods have little reason to pay attention to what is spoken there.

Gods can speak directly to their oracles.They can appear in the dreams of mortals or manipulate natural phenomena to create omens. They can also create Nyxborn creatures to serve as messengers or emissaries.
Gods grant their clerics the ability to cast spells, and they can effortlessly duplicate the effect of any spell they could grant (any spell on the cleric spell list, as well as any domain spell from their domains). They also have broad influence over aspects of the world associated with their portfolios, beyond what can be defined by spell effects. For example, Purphoros can make a volcano erupt, and Thassa can call up a tidal wave. Gods can bestow supernatural blessings on mortals, and they can lay terrible curses (such as when Mogis turned a herd of cattle into catoblepases).

The gods can assume any form they choose. They most commonly appear as humanoids - the form in which the people of Theros most easily imagine them - but on an enormous scale. They often seem to be walking across the dome of the sky. with their feet disappearing just below the horizon. Any part of a god's body that isn't directly lit takes on the appearance of the starry night sky of Nyx. The gods sometimes also appear as animals or magical creatures, or they manifest in insubstantial forms like sunlight or wind.

When physically present in the mortal world, a god is capable of devastating physical attacks. Heliod's spear striking the polis of Olantin caused it to sink forvever into the sea, and an errant blow from Purphoros's hammer shaped the mountains.

The power of the gods exceeds that of any mortal being. Even so, a god killing another god - let alone a mortal attempting the task - is virtually inconceivable. Any kind of direct confrontation against a god by mortals would require the assistance of at least one other god, and ideally more than one, to have any hope of success. A group of adventurers might try to convince a group of gods to lend their aid against a god who has become a threat to the mortal world, hoping to get the gods to band together to restrain or punish the offender.
Kruphix or Klothys might be able to force a god into a physical form that doesn't fill the sky (perhaps something similar to an empyraen or the terrasque), which could enable adventurers to battle the god, especially if they have access to a divine weapon like the artifacts detailed in chapter 5. But defeating the god in that form would merely weaken the deity, allowing other members of the pantheonm to capture, bind, or punish them.

Divine Relationships

The pantheon of Theros is a family - a large, often dysfunctional family rive with petty jealousies and rivalries but also held together by genuine affection, admiration, and cooperation. It is easiest, after all, for mortals to concieve of gods that are very much like themselves, and the gods of Theros are very humanlike in their foibles and their exploits.

The pantheon of Theros has expanded though four generations of divine evolution. Some tales describe these as actual generations, suggesting (for example) that the storm god, Keranos, is the literal son of Thassa, god of the sea, and Purphoros, god of the forge. Others describe the generations in metaphorical terms, suggesting that Keranos represents a combination of Purphoros's creative energy and Thassa's deep knowledge, resulting in lightning-like flashes of inspiration (as well as the fury of a physical storm). In all their various forms, though, the myths agree on the basic structure of the pantheon's development.

The time of the first generation precedes the presence of what are commonly understood to be "gods." Before mortals dreamed the gods into being, before they could even imagine beings as noble as the gods, the malleable dream-substance of Nyx gave shape to their fears in the form of the titans.

The titans were beings of utter chaos, representing everything that stands against order in the mortal worlds, never worshipped but sometimes appeased. Myths recount how the gods battled and imprisoned the titans, sealing them in a prison beneath the Underworld. Now the titans are all but forgotten in mortal imagination. Scant mention of their names and epithets appears in the oldest tales, hinting at the nightmares that birthed them.
Kroxa, Titan of Death's Hunger, embodied the terror of death - and its insatiable gluttony for new creatures to consume. Uro, Titan of Nature's Wrath, might be seen as the direct predecessor of Keranos and Thassa, but it was the incarnation of natural disaster, having none of the creativity and thoughtfulness of those gods. Phlage, Titan of Burning Wind, was an all consuming whirlwind of fire, and Skotha, Titan of Eternal Dark, was the utter darkness of the starless night.

The oldest of the gods, and often imagined as siblings or as some king of offshoot of the titans, are Kruphix and Klothys. The origin of this second divine generation is mysterious. Perhaps Klothys arose from a sense of inevitability, a notion that the world was unfolding as it must, and thus the actions of mortals made little difference. Kruphix might have been born from a sense of mystery, supporting the idea that the workings of the universe are simply incomprehensible to mortal minds. It's also possible that Kruphix and Klothys are a different order of beings from either titans or the other gods, and Klothys at least has existed for unknown ages despite being all but forgotten among mortal folk.

Once mortals could imagine a world beyond the horizon and a course of destiny that left behind the trials of life, they could formulate the notions of principles, order, and natural law. Out of those ideas, the third generation of deities was born: sun-crowned Heliod, deep-dwelling Thassa, bleak-hearted Erebos, bronze-blooded Purphoros, and keen-eyed Nylae. These gods are known to refer to each other as "brother" and "sister," though they never speak of parents and almost certainly don't imagine Kruphix and Klothys in that role.

The other eight deities, the fourth generation, represent the application of abstract principles to the reality of mortal life. For example, while Heliod stands for universal moral precepts, Ephara is the god of laws, the rules and structures that govern mortal societies. Nylae is the god of wild nature, predatory animals, and the change of seasons, and at the same time Karametra is the god of nature tamed for human use - agriculture and domestication - and of the natural cycles involved in human life, especially childbirth.

These gods recognize the previous generation as their elders but only occasionally as parents. Iroas and Mogis are widely considered to be brothers, but few myths describe their parentage, and those that do contradict each other - in keeping with the nature of these eternally warring gods.

Myths and Deeds

Countless tales tell the history, deeds, and nature of the gods. Sometimes these stories play out among the constellations in the night sky. They are chanted in hymns during the gods' festivals, inscribed in temple walls, told around campfired and hearths, and collected on scrolls. Some are simple fables meant to illustrate a single facet of a god’s character or of moral behavior. Others are monumental epics, most notably The Cosmogony, a poem by an unnamed Meletian sage that includes several (sometimes conflicting) tales of the creation of the world and beyond.

The people of Theros don’t balk at contradictory myths. Is Keranos the literal child of Thassa and Purphoros? Did he spring unbidden from Thassa’s heart when her rage grew too great for her to control? Or did he come into being when Purphoros tried to steal the secrets of Kruphix? To the people of Theros, it doesn’t matter whether these tales describe historical facts, and each of them is true in its own way. Each tale about Keranos expresses a truth about the god, about inspiration and storms and secrets. Studying each one can lead Keranos’s worshipers to a deeper understanding of and a closer relationship with their god.

Various writings, usually organized around a central theme, collect myths about the gods. The Origin of Monsters is one such collection, notable as an attempt to find commonality in a number of different tales about the birth of dragons. It also describes how Pharika hid secrets in the blood of basilisks, how the spirits of great warriors are reincarnated in the form of manticores, and dozens of other tales.

The epic poem called The Theriad is another such collection. It describes the exploits of various champions of Heliod, all of whom are simply called “the Champion,” as if they were a single individual. Because the identities of the heroes aren’t mentioned, the tales have more to say about the character of Heliod than about any champion’s mortal deeds.

The Callapheia, by contrast, is about the exploits of a single mortal hero, Callaphe the Mariner, who snuck into Mount Velus and stole Purphoros’s tears, hid behind Phenax and wrote down his secrets, and raced Thassa at the edge of the world before sailing into Nyx. Tales of this sort highlight the gods’ pettiness and vanity and promote the somewhat blasphemous notion that a mere mortal can outwit the divine. The Callapheia also serves as something of a gazetteer of Theros, describing its various lands and their inhabitants, at least as they existed some centuries ago.

Finally, the deeds of the gods are sung in paeans during their festivals. Naturally, these hymns portray the gods in the most favorable light, as benevolent (or at least indifferent) and all-powerful.