Abeir

Abeir was the twin planet of Toril, located in the same material plane of its sibling world, but within a "pocket dimension" that was out of synchrony with Toril. Abeir revolved around the same sun of Realmspace, although from Abeir the sun was seen as blue colored. Abeir shared the lunar satellite Selûne and its Tears with Toril.

Geography
Abeir had steel-colored sky due to the arambar, the residue energy left by the death of the primordial of the same name.

The only known continents of Abeir were Shyr and Laerakond (at least before it was transferred to Toril). For a time, Maztica was also part of this world. Like Toril, it also contained an Underdark.

The original kingdom of the Abolethic Sovereignty was also located in Abeir.

Inhabitants
Abeir was inhabited primarily by primordials, dragons, dragonborn, dwarves, genasi, halflings, humans, and a few other races that also inhabited Toril.

Elves and other fey creatures were almost unheard of in Abeir, although drow were known to inhabit its Underdark.

Abeir was also inhabited by abominations and other aberrant creatures from the Far Realm, most of them the original inhabitants of Abeir-Toril.

Magic
Magic manifested differently on Abeir than in Toril, as there was no Weave and no normal ways to contact any gods, as gods were wary about this world. Likewise, Planar magic (or at least planar magic that depended on the Nine Hells), such as that granted to warlocks by a pact, also worked differently and was more difficult to use than in Toril.

The only magic that worked normally on Abeir was that a creature could create on its own, such as the inherent elemental magic a primordial had in its body or a dragon's breath. Magic items also worked normally on Abeir, and Abeiran dragons usually scavenged primordial corpses in order to create powerful artifacts from their remains, such as the Breath of Petron.

Creating artificial portals to Abeir was nearly impossible, but a few natural portals connected Abeir and Toril.

History
After Ao sundered the world of Abeir-Toril, splitting it into the two twin planets, Abeir and Toril, he gave Abeir to the few primordials who survived the Dawn War to rule. Those primordials were tired of war and were unable to overcome their dragon steeds when those rebelled against them, starting the conflict known as the War of Fang and Talon. After the war the few primordials who survived retreated into hiding and fell silent, and only a handful of dragon lords survived. Not long after, a mighty dragon called Gorloun founded the first dragon empire, and soon rival draconic realms sprang up thereafter, and the long Rule of Dragons began. In the lands of the eastern continent Shyr, the despotic primordial Karshimis also created his own nation.

These nations quarreled each other for ages, but draconic rule remained nearly unchallenged until the Blue Breath of Change, when both worlds merged for a certain time. Laerakond and other regions of Abeir were transported to Toril, and the fate of the remaining nations in the world of Abeir became a mystery to Faerûnian sages.