I’ve also read that it could be some sort of an Avatar of Emrakul. It’s from the story “the hand that moves” where Emrakul appeared to Nissa in the trail of Knowledge.
https://magic.wizards.com/en/articles/archive/magic-story/hand-moves-2017-04-26Quote:
She saw a young man, his face erased, stumbling among a garden of statues. High above the man a growing cloud of dusk attacked the sun. From somewhere outside the garden there was a mighty roar.
Shift.
Nissa saw a world, then tens of worlds, hundreds of worlds. Thousands. She saw this world, the world of Amonkhet, and wrapped around it was a dark sinewy line. That line stretched back through all the worlds, all the thousands of worlds, and she saw an unbroken line of darkness from Amonkhet all the way back to the beginning of the line.
Shift.
A large golden disc, shaped and stylized like a sun, descending from the sky. The sun disc approached a large circular stone tablet covered with strange sigils, and the two discs merged, becoming a single golden disc. Cracks appeared in the golden disc, small at first, then widening, growing. The disc crumbled away into nothingness.
The scenes shifted faster now, barely even an image forming before being replaced. A fizzling torch. A broken clock with a clean face. A mummified head facing backward atop a mummified body. A split tree, its sap oozing into the ground. A shattered shield, its shiny metallic pieces torn and scattered.
She closed her eyes against the onslaught, but still the images came tumbling through her head, crumpling her in mid-air. A falling dragon. Giants, covered in metallic blue, stomping through streets. A massive flash of light, consuming a world.
An angel descending from the sky.
Nissa opened her eyes, and the angel continued to descend. It was the angel from her nightmare. The angel that reminded her of Emrakul.
The angel's eyes were open, but unlike the dream, there were no snakes, just blank white orbs. She landed in front of Nissa.
"Why do you dally? I showed you the ways of power. Use them." The angel's voice melodious, a cool breeze. Beautiful. And beautiful the way Amonkhet was beautiful, all horror underneath.
There is some foreshadowing on those scenes. Makes me wonder if the wanderer is some kind of angel, she looks a lot like Avacyn but she was unmade by Sorin though. The falling dragon could be Bolas or may be Niv-Mizzet