Avatar
When creation came to be from the Eldest weaving parts of the Sea of Chaos into ordered worlds, they also created Gods to look over those worlds and act as their servitors. Beings of untold power and might, the Gods would be locked away in incorporeal forms which could traverse between the realms of Auria and the Afterworld at will, using the powers granted to them by their gods to continue spinning the gears of creation without revealing themselves to the Mortals who they served to preserve.
Whether it be a deep-rooted desire left behind from the Cosmos' influence or simply independence made manifest the Gods would not stay hidden from Mortal eyes for long when Unysta, Goddess of Dreams and Mistress of Shapes devised a means of using their divine magics to create corporeal forms in which to walk the lands of Auria which they so endlessly labored for. Calling these forms Avatars, the Gods could travel from the Afterworld onto Auria and show their presence upon both Mortalkind and Beastkind, sprouting the first tales of religious worship among the mortals when they witnessed first hand the radiance which the Gods represented and wielded.
Though they were now free to walk the corporeal world freely, the Gods understood that they cannot truly live among Mortalkind lest risking their powers be used selflessly, prompting them to reduce their physical visits upon the Planets to a rare occasion. Furthermore, the Gods understood that when they walk the lands as Avatars, their duties of watching over Auria's existence from the Afterworld remains dormant until they return, which has also led them to establish laws to stagger when a God may use their Avatar form as to not have too many of them away for too long.
The Avatar Forms have been used by Gods many of times throughout history - Fenros is known for using his Avatar to come down to Gwynbrenon and appear in front of the Wylderin
Technicalities
The spellwork to create an Avatar of oneself is similar to that of Shapeshifting - Using an extraordinary amount of Ether, the spellcrafter creates an corporeal form of themselves which they may then embody. However, the difference between Shapeshifting and Avatars is that while Shapeshifting creates an alternative form for a Mortal being, Avatars must create a Mortal form which did not exist previously. As such, Avatars are able to exist like any other living being and no amount of Anti-Magic is able to take them out of the form.
Though Avatars house the soul of Gods within them, they are specifically designed to limit the powers of the God within whilst they inhabit the body, lowering the capabilities of Avatars to the levels of Dragons at best. This allows Avatars to experience the world they watch over from Mortal perspectives, allowing them to learn from them in many ways. Multiple reasons are given for this limitation
1. Mortal bodies are only able to hold a limited amount of power within themselves.
2. The corporeal realm cannot withstand the full potential of a being on the scale of a God existing within it.
For a God to turn into their Avatar, all they must do is follow the same process as what Shapeshifters do - Think of their form which they have created and transport their being into it. However, Gods also utilize a location which they have each specifically chosen where that Avatar appears every time they wish to walk the lands of Mortals once more, transporting their Avatar to that location every time they assume the form.
Though it has happened only a handful of times, Avatars can be defeated by Mortals due to their limited powers and even "killed" to an extent. Stories among the Humans, Enkhulu and Hayka tell of epic battles where many dozen of Mortal warriors came together to do battle with a God made Mortal and slay them much like one would raid a Dragon's lair and kill the Dragon within. Fortunately, the soul of a God cannot be so easily destroyed and when their Avatar falls, they merely return to the Afterworld without any harm to their being, although their Avatar form does require recuperation before it may be used again.
Though Avatars are primarily utilized by Gods, it is not uncalled for Mortals to also create their own Avatars however no such record has yet to be shown due to the otherworldy amount of power one must hold to be able to create an Avatar of themselves and the usage of one is often counterproductive considering the main use of Avatars is to walk the world in a Mortal body.