The Spelljammer

The Spelljammer is a living vessel, miles across and with a small city across it's back. It has been sighted throughout history at moments of great change - sometimes a portent for good, but more often seen as an ill omen. It is shaped similar to an enormous manta ray, with it's tail curved up behind it and pointing forward over its head, like a scorpion.
Little is known of the city upon the vessels back, nor the occupants of the city - although those that have flown close enough to see with telescopes claim they have seen all races present (and even some unknown ones besides). Some tales have claimed the cities' occupants fight with each other, but in most cases it appears they defend their city from anyone approaching, firing upon nearby vessels without provocation.
The following rumours have been given credit in academic circles, using scientific enquiry:

• It is a singular being - it is never seen with others of its kind

• It has been killed multiple times, and reappears within several hundred years

• Only great fleets, apocalyptic magic, and divine intervention have been able to defeat the Spelljammer

• When defeated, the vessel is consumed in a powerful explosion

• The vessels primary means of defence appears to be the occupants of the city on its back

• On occasion, The Spelljammer has been seen to fire enormous balls of energy from its raised tail section

• One three recorded occasions, prior to its destruction, The Spelljammer has been thought to 'spawn' smaller versions of itself. This has lead to a theory that one of these offspring grows to be a 'new' Spelljammer, but has not been proven concisively

• No magical, psionic, or divine clairvoyance or prognostication is able to sense The Spelljammer

• Prior to The Shattering, The Spelljammer opened immense portals in the sides of crystal spheres. Some of these portals persisted long after the ship had moved on, with the longest open for a period of three months

The following rumours have not been validated, but persist in less scientifically rigorous tales:

• The Spelljammer birthed every crystal sphere, including their gods and powers

• Every spelljamming helm carries a small piece of The Spelljammer inside it

• It caused The Shattering (and/or any other cataclysmic event across wildspace and the known worlds)

• It ended the Tyrant Era

• Every sapient being in the known multiverse is somehow physically related to The Spelljammer

• Anyone who breathes the air of The Spelljammer becomes instantly enslaved by it, becoming its crew

• An ancient, undying lich is the pirate captain of the vessel, and uses it to cause havoc

• It is the scale of an incomprehensibly large dragon, who guides it through the systems from afar, like a child playing with a rock and marbles

• It feeds upon the living, sweeping them up into an enormous maw on its underside

• It is an ancient weapon of one of the Beholder nations, and even now it obeys their mad commands

• It is the enemy of (insert any spacefaring god or ascendant power here), pursuing them across the multiverse

• It is the shepherd of every spacefaring god or ascendant power, and they are as its sheep.

• In the Era of Myth, the Spelljammer was covered with an enormous turtle shell, made from the same material as the crystal spheres. Each time it molted, the molt became a new crystal sphere

• The city on its back was originally capital of a groundling nation, who left their planet behind aeons ago

• The cataclysm of Krynnspace was caused by The Spelljammer crashing into Ansalon

• The ancient Elves of Myth Drannor moved their entire civilisation onto its back thousands of years ago

• A powerful psionicist became The Spelljammer when they lost control of their psychometabolic powers

• It isn't real, it's a cleverly disguised tinker gnome vessel, with thousands of yards of cloth and supports to make it look bigger

• Its stomach contains more riches than every groundling and spacefaring nation rolled together, a dozen times over

• It is the result of a poorly worded wish spell

The Felljammer

Rumours persist of a Felljammer, potentially related to the Spelljammer. In 2961 Aurora discovered the journal entry of a deceased Astral Elf in the Tomb of the Nine Gods, with some leads on The Felljammer's whereabouts and history.
012 Felljammer

Confirmed Spelljammer Sightings:

Spelljammer Sighting: Chik'thik'kal
Spelljammer Sightings across wildspace
Spelljammer Sighting: Seldarspace
Spelljammer Sighting: Realmspace
Spelljammer Sighting: Realmspace
Spelljammer Sighting: Ragespace
Spelljammer Sighting: Greyspace
Spelljammer Sighting: Krynnspace
Spelljammer Sighting: Scrospace
Spelljammer Sighting: Greyspace
Spelljammer Sighting: Krynnspace

Confirmed Felljammer Sightings

Felljammer sighting, Krynnspace
Felljammer sighting, Greyspace
Felljammer sighting, the Phlogiston
Felljammer sighting, Ragespace
Felljammer sighting, Realmspace