Planeswalkers

The defining trait of planeswalkers is the ability to travel between separate universes with ease, while the vast majority of people throughout the multiverse are not even aware that other worlds exist besides their own. Planeswalking is a form of magic. With enough time and mana, or with specialized spell knowledge, or with access to enormous power, it's possible for a planeswalker to transfer clothing, artifacts, and/or creatures with them as they planeswalk.
A planeswalker is specifically a being who possesses a planeswalker's spark, an imprint of aether on a being's soul. One in several million sentient beings is born with a planeswalker spark, and having it ignite is exceedingly rare. Some number of these die shortly after completing their first planeswalk. There is only an incredibly remote chance that any given sentient and natural being is born with a planeswalker's spark.
Planeswalkers can be born at random, with no outward signs of their latent power. Such a being is called an "ember". Fewer still will ignite their spark. When an ember is put through a period of extreme stress or strong emotion, the spark can trigger, causing the individual to ascend and become a planeswalker. Ignitions are often caused by near-death experiences, though it is possible for an ember to undergo such an experience — even dying — without igniting their spark.
Notable Planeswalkers include Lilliana Vess.