The Third Races

Thanks to u/ArtofEde from Reddit for the grim cover art!

"We will never again be slaves to this Eternal Design! We, the gith people, shall rise to our own occasion! Break free from our fetters, and bring ruin to those who gave us our place!" -- Pidreth, proponent of the Great Schism of the Gith and first githyanki Warmother

The Third Races are those that came about during or after the Reckoning. The vast majority of these creatures will have arisen in the Reckoning itself, but a handful of species -- playable and otherwise -- have arisen over the course of the Age of Extant. As with the First and Second Races, this article primarily serves as the hub for the more in-depth playable race articles, as well as a compilation of short excerpts regarding the non-playable types of creatures that arose during this time period.
Many of these creatures were directly created for warfare or were spawned as a by-product of it. When the Reckoning's flames consumed Yophas, an unimaginable amount of life and knowledge was lost. But, from the ashes -- or the flames themselves -- many new things were found.

Those Who Rose in the Reckoning

The Reckoning was a prolonged period of divine warfare that had major campaigns across all of Yophas. The gods -- and their powerful followers -- pushed the limits of arcane and divine experimentation to create beasts of war. For this reason, many of the creatures that came about during the Reckoning are, to this day, some of the most dangerous creatures that can be encounter on Emaxus or beyond.
There are also a few races that have come about in the Age of Extant, either as a result of prolonged exposure to the effects of the Reckoning or by other means. Those can be found at the bottom of the list below.

Magical Abominations

During the Reckoning, there was a widespread employment of magically-created abominations. Typically fusions of different predators, these differed from the chimaeric fusions of the Age of Rebirth in that, beyond being grafted together, they were further enhanced by way of forced evolution. A feline predator could be evolved into a sleek assassin with the ability to turn invisible, or a mammoth could be fused with the genes of a devil to create an infernal war beast. The possibilities were truly endless, and though almost none of these creatures are still being created, a dangerous amount remain spread across Yophas.

Divine War Machines

Similarly, the gods and their creations set about furthering the capabilities of divine warfare. To this end, not only were new angels and other celestials created, but divine war machines began to be invented. From monolithic constructs of war to tiny mechanical wasps capable of wholesale slaughter, the gods set about creating many horrid machines of massacre. Chief among the propagators were Kaedo, Narvox, and Laaelum, who set about inventing and creating new tools of death with earnest -- albeit the former was more solemn about it than the latter.

Mutants

With the titanic amounts of magical death-dealing that was done during the Reckoning, many locations were permanently changed by the God-Wars. Whether they were destroyed, corrupted by arcane radiation, or something else entirely, many of those locations inhabitants that didn't die outright found themselves mutated by the fallout of the battles. Many strange species that have arisen in the aftermath of the Reckoning are mutants created in this way, like the falarak in Drumis.

Ix'akrothian Hordes

One of the most terrifying sources of new species during the Reckoning was the hordes that came spilling out of Ix'akroth. While new demons and other swarming creatures had already been arising in the Infested Crags, once Ix'kythael arrived and began creating planar armies in earnest, she began creating countless new swarming creatures. Hybrids between demons and other creatures, evolutions of different beasts, all in the name of her ever-sprawling broods.

Those Who Rose After

Below are the handful of non-playable races who have arisen in the Age of Extant (excluding the Mutants above, who have continued to evolve due to the radiation and such).

Necroficial Creations

The main development during the Age of Extant has come from the necroficial monstrosities created by Krathum the Defiler. Though primarily consisted of the Undying -- the monstrous, necroficial army of undead that Krathum unleashed near the end of the Fragmented War -- necroficy has evolved much since then. Handfuls of these creations still roam Aitreas, and handfuls more continue to be created by mad scientists and the like.

The Third Race: A Pocket Guide to the Playable Options

As with the Second Races, these are only races that are so different from their progenitors (or lacking in progenitors) as to be considered completely new. Subraces created during this time period are denoted as such in their overarching racial articles.

• Bugbears: Bugbears were created by Marzak through the fusion of orc and firbolg blood, making powerfully built and strong warriors that were naturally deft.
• Goblins: Created by Ix'kythael, goblins were a fusion between orcs and insects: smaller, more plentiful, and prone to swarming.
• Hobgoblins: Created by Narvox, hobgoblins were a fusion between orcs and humans, meant to be able to create large units and be tactically brilliant but martially powerful.
• Githyanki: During the Reckoning, a great schism rocked the Gith people. The Githyanki were those who swore themselves to the Obsidian Lords, becoming tyrants and warbands that roamed Ipacia.
• Githzerai: On the other side of this schism, the Githzerai were those who stayed loyal to their original purposes, continuing to hone their psionic control over the Realm of Stars and defend it against malefactors -- including their old brothers and sisters.
• Dhampirs: Dhampirs were created by Laeelum when she sought to create weaker but more plentiful vampires.
• Hexbloods: Hexbloods were created by Syluru to be fey supersoldiers. Now, fey have taken the originally divine magics and twisted them to continue creating new hexbloods.
• Yuan-ti: Yuan-ti were a fusion between human and snake created by Ix'kythael to give her plentiful soldiers for her armies.
• Warforged: Warforged are the only known race to have come about in the Age of Extant, having been invented by the Imperium. They were created by way of fusing artificially created, arcane souls with bodies made of metal and living wood.