Materials from almost all officially published WotC material are available, though some have changes listed in these rules. All UA material, Stream content, and any features that are setting-specific require DM approval and possible modification before using.
All material from the Astral Adventurer's Guide (AAG) can be used to create a spacefaring character, with the changes outlined below.
Items not from official WotC material require heavy DM scutiny to be accepted, and may be reworked on the fly.
All official and homebrew material allowed in any setting can be used when creating a character who is already an experienced spacefarer. However, if making a character with multiple materials that are setting-exclusive, it is expected for some level of consistency to be maintained. When you create a spacefaring adventurer, choose a setting detailed in this document. You must follow the character creation rules of this world, and your race must either be one allowed in that setting or one from the AAG.
While most individual settings may give double EXP for interacting with a specific pillar of gameplay in order to encourage a particular playstyle while within its sphere, Voidspace adventures grant EXP evenly across all encounter types.
Each universe has its own connection to its own set of planes. Voidspace has no connection to any of them. Most adventurers do not immediately think this is a big deal, but it has a lot of unforeseen ramifications:
Summoning spells do not function in Voidspace, including spells that draw energy from other planes.
Spells and Magic Items that rely on demiplanes or pocket dimensions do not function in Voidspace. Leaving a universe with an item such as a Bag of Holding will cause the items within to scatter onto that universe's Astral Plane, as if the item was broken.
Spells that allow for planar travel or that allow contacting extraplanar beings do not function in Voidspace.
Clerics, Warlocks, or any other class which gains its power from an extraplanar entity, are not able to level up or change their prepared spells in Voidspace.
Once in a new universe, however: if an equivalent entity exists in an alternate world, it may be possible to convince that entity to honor an established relationship from your original world. For example, a cleric of a Time deity in one universe could pledge themself to a similar Time deity in a new universe, or a warlock of Dispater could present their contract to the Dispater of a different universe.
When a creature dies in Voidspace, their soul has no god to claim it, and no afterlife to be drawn towards. It remains in the void as an incorporeal Undead creature of the DM's choice, usually a ghost. Resurrection spells only function in Voidspace if the soul is within 60ft of the body during the casting of the spell. If the undead remnants of a creature's soul are destroyed, that creature cannot be resurrected by any means.
The spheres are so far apart, it takes light itself years to travel between them. The only reason ships can travel between them at all is because of the way in which Spelljamming Helms take advantage of the innate powers of phlogiston.
Phlogiston is a highly flammable gas that flows in rivers through Voidspace, linking nearby crystal spheres. Depending on the distance and position of the spheres, the flow may be faster or slower in areas, allowing for different speeds of travel depending on which path is taken.
If a tiny open flame or spark ignites a river of phlogiston, it creates an immediate explosion. Spells that deal fire damage immediately explode as soon as their path touches phlogiston, and do so with triple the diameter as normal.
If phlogiston gas is somehow captured and brought into a crystal sphere, it will immediately dissipate into elemental chaos.
Different areas of Voidspace have different amounts and types of air. Some objects floating through the void have a breathable atmosphere; others are surrounded by toxic gas. Phlogiston tends to flow through areas of vacuum.
A creature who breathes phlogiston gas immediately begins suffocating. If a creature suffocates in phlogiston, they do not die. Instead, they are Petrified until again exposed to breathable air.
Within Voidspace, every creature and object has its own gravitational pull, which extends outwards a distance equal to the object's radius. Most objects' gravitational fields pull towards the center of the object, but this can vary a lot, especially when magic is involved.
Spelljammers usually have their own gravitational planes, depending on the helm and ship. Most spelljamming helms create a single gravitational plane bisecting the ship halfway down. Custom-made spelljamming helms can create a more specific set of gravitational planes for the ship it is installed into.
If a creature or object is Huge or larger, this pull is strong enough that smaller creatures can walk on it. If multiple gravitational fields overlap, only the strongest pull matters.
Hadozee: After using your reaction to Glide, you can choose to descend at any rate from 10ft per round to 100ft per round, moving horizontally a number of feet equal to your walking speed on your turn each round until you land. Descending faster than 100ft per round will cause you to take fall damage. If you take any action that requires the use of your limbs while gliding, you must use your reaction to initiate another Glide to prevent falling.
Giff: Firearm proficiency is a cultural trait, not an innate one. That being said, Giff spacefarers really tend to love their guns.
Create Spelljamming Helm: This spell does exist, but is a closely guarded secret of the Mercane race. It cannot be learned at character creation or level-up, but it may theoretically be learnable in-game under very specific circumstances.