The Astral Sea 

A pale, sourceless blue light bathes this world of worlds. It stretches out to infinity, but it’s also the local neighborhood. Every known world comprises a speck in its murky expanse, yet everything that exists is next door through the Astral Sea. 

The Space Between 

The Astral Sea surrounds and contains entire worlds suspended within it. Every space in the Beast World has a corresponding one in the Astral, but at an inconsistent scale. A closet in the Beast World could be a vast Astral horizon or a miniscule dot. Astral space warps and resizes when observed, allowing teleportation and plane shifting in the Beast World. Using magic to reduce the Astral distance between two points in Beast World space, one can instantly jump into the Astral and back again to skip the journey. 

This also allows one to travel there; when a creature in the Beast World uses any kind of teleportation magic without designating a destination, the resulting “error” is a trip to the local Astral Sea. The creature can later return by the same method. Not all teleportation magic allows one to forgo a destination, but a specialized version of dimension door is the simplest method. 

Swimming in the Astral Sea 

When a beast wills themselves to travel through the Astral, their mind warps intermediate space to “move” them in whatever direction brings them closer to their destination. Bats are accustomed to this mode of travel and can slip through the Astral as if flying. 

Mental movement is based on point of reference. If a creature shifts to a random point in the Astral Sea, it’s nearly certain there will be nothing within sight. Without an object to concentrate on, motion is impossible. To get around, many Astral travelers carry a magic item called an astral anchor. 

This mental movement only applies to creatures and objects with Intelligence scores Missing your longbow shot in a bat city is much more dangerous. Objects propelled through Astral space continue moving until stopped. 

For Players. 

Astral Anchor 

wondrous item, common
As an action, you can speak its command word to make this ½”-diameter copper marble shed bright light in a 20-foot radius and dim light for an additional 20 feet. The light is a red-orange color complementary to the Astral Sea’s blue, visible up to 10 miles away if unobstructed. Completely covering the marble with something opaque blocks the light. When you use an action to speak the command word again, the light is extinguished and the marble appears in your hand. 

Almost Empty, But Only Almost 

While knowing the destination is the easiest (i.e., only reasonably possible) way to find things in the Astral Sea, the wobbly space has many bizarre things floating within it. Regions coterminous with another world are the most common sight in the Astral Sea. Stretched, ethereal representations of Beast World places drift through the blue expanse. Sometimes they’re tiny and sometimes they’re the size of entire continents. When someone uses magic to make themselves ethereal, such as when casting etherealness, these coterminous spaces are dragged together around the user, then dissipate when unobserved. 

The Beast World recently learned there’s at least one species native to the Astral Sea: the bats. Their cities are vast, bizarre mazes of astralcrafted buildings floating at disparate angles. They stay in contact using lighthouses to provide crucial points of reference networking their civilization together. 

Every “extraplanar” space in the Beast World is actually an Astral space, pulled together and held in place by magic. The assurance an intruder won’t wander up to a secret chest or bag of holding is sheer unlikelihood—even if a spell could detect an object a million miles away, blind searching would never find even one such space. Even knowing its exact location wouldn’t matter, as there’s no way to know one is traveling in a straight line across such distances. 

Falling Up 

Gravity occurs in enclosed spaces in the Astral Sea. Astral gravity is based on the consensus of creatures and objects. When a space is enclosed for the first time, there is no gravity. Whatever direction is “down” to most entities becomes down. 

Unattended objects in a room with gravity count as one entity for every size category they are above Tiny. A creature is treated as a number of entities equal to 1 + its Intelligence modifier (minimum one). If gravity changes in an enclosed space, all the creatures and objects within “fall” at a rate of 60 feet per round and do not take fall damage. Gravity cannot change in a space more often than once per minute. 

For example, a bat with an Intelligence score of 10 is sitting in her bedroom, which has a Small nightstand and a Large bed. Her three cruel-but-brilliant brothers each have an Int score of 16. They enter together and “decide” that the ceiling is down. They are treated as 9 entities (three creatures with +3 Int modifiers), while she and the objects in the room are treated as 5 entities (A Small object counts as 1, a Large one as 3, and she counts as 1). The bed, the nightstand, and all the bats drift toward the ceiling. 

Material and Mind 

The strange matter that makes up the Astral Sea is called astra. Its normal state is a breathable, air-like substance which rests at 70 degrees Fahrenheit. With practice, a clever beast or brethren can do more with astral than stretch it to carry them toward. Mental discipline and the ability to picture an object in one’s mind allows one to create solid objects from astray, without regard for the limitations of space or materials. The skill of creating material objects from astray is called astralcraft.

The possible creations of astralcraft are limited only by imagination. Physical properties such as color, hardness, size, and complexity are all dependent on the crafter’s ability to manifest these properties in their mind’s eye. Raw intelligence also governs a creation’s function, as well as how long it lasts before drifting back into the vaporous astra which surrounds it. 

Anyone in the Astral Sea can conjure an amorphous bubble of mass, but geniuses of astralcraft can paint cathedrals in thin air, visualizing every brick and plank. These creations last for weeks, and the master astralcrafters among bat-kind can render an object from astral permanently. 

Astra cannot exist in other worlds. When a conjured object leaves the Astral Sea, it vanishes instantly. 

For Player. Astral, Ethereal, Shadow... 

The Beast World setting uses the Astral Sea to represent both of 5e’s “Transitive Planes” and one other: the Astral Plane, the Ethereal Plane, and the Shadowfell. When a spell or effect in 5e refers to one of these planes, treat it as referring to the Astral Sea.

Astralcraft Rules 

With 1 minute of concentration, you can create physical objects from astra in an unoccupied space you can see. Roll an Intelligence check. Use the result of the roll and the Astralcrafting Limits table to determine what you can create. If you attempt to create something you’ve made successfully at least twice before, or create a copy of something you can see and touch while concentrating, make the Intelligence check with advantage. If you fail to meet the DC to create the item as intended, you can instead create a less complex or less durable version of the item, according to the result. 
Objects made with astralcraft can be carried and worn as long as they exist, but disappear immediately if removed from the Astral Sea. 
Magic. By expending a spell slot and spending an extra 10 minutes concentrating, you can use astralcraft to create a magic item that you have used at least once in the last year. The DC is 20 for common magic, 25 for uncommon magic items, and 30 for rare magic items (rarer magic items are impossible to make from astra). You must expend a 3rd level spell slot to attempt to make an uncommon magic item, and a 5th-level spell slot for a rare one. Astralcrafted magic items turn back into astra if their creator attempts to create a new one, or after 8 hours. When relevant, astralcrafted magic items: 
  • Have enough charges to produce their most expensive effect once 
  • Cannot be copied into a spellbook, if they are scrolls 
  • Cannot create ongoing effects which last longer than the item exists (effects with longer durations end when the item disappears) 
  • Cannot target or affect anything outside the Astral Sea, or transport anything to a different world 
  • Grant temporary hit points whenever they would otherwise restore them, which are lost when the item reverts to astra or when the creature leaves the Astral Sea 
  • Suppress conditions and other effects instead of removing them (such as from restoration). The time suppressed does not count against the effect’s normal duration. 

Comestibles. Only bats and other creatures native to the Astral Sea can sustain themselves on food and water made from astra. The DC to decide an item’s taste is 15. 
Hasty or Careful Creation. You can sacrifice some control to use astralcraft quickly, or focus for longer to create more complex objects. If you astralcraft as an action, subtract 5 from the Intelligence check’s result. Items created this way can only exist for a maximum of 1 minute, and magic items cannot be created this way. After making the Intelligence check to create an item, for every hour you spend concentrating afterward, add 1 to the result. Treat this the same as concentration on a spell. If you stop concentrating on the item, the result is decided. Extra concentration cannot be used to meet the DC for the creation of a magic item. 
Damage. Objects created with astralcraft that deal damage of a type other than bludgeoning, piercing or slashing (such as a pool of lava) can deal damage up to the creator’s Intelligence check result - 10 per round. For example, if a creature is thrown into a barrel of acid made with an astralcraft check of 16, the acid can deal up to 6 damage per round. 
Value. Astralcrafted items have no gold piece value for the purposes of spellcasting