Planeswalker

A planeswalker is a being whose innate "spark" has been awakened. Only a planeswalker can travel from one plane to another. Planeswalkers are always sentient and are almost always naturally talented spellcasters. They range from neophytes who know only a few simple spells to ancient archmages with a vast magical arsenal at their command

For millennia, being a planeswalker meant having inherent godlike power—so much power that planeswalkers' sanity tended to erode over time as they became more and more unable to identify with the cares and concerns of mortals. During this time, planeswalkers could move between planes with a thought, in an instant. They were ageless, could take any form they wished, and could call upon unimaginable amounts of mana to work magic. Planeswalkers didn't require food, water, air, or sleep. They could create and destroy entire planes of existence.

But this near-omnipotence caused the Multiverse itself to become unstable. As more planeswalkers fulfilled their potential, more of the chaotic energy of the Blind Eternities came to exist within the planes themselves. More importantly, when planeswalkers fully exploited their connection with the æther to wield cataclysmic magic, the fabric of the Multiverse itself began to tear under the strain. This led to a state of increasing temporal and planar entropy.

During the temporal crisis on a plane called Dominaria, as planeswalkers began to willfully rescind their sparks to close the rifts, the Blind Eternities began to pull the spark back into the æther like a drain sucking in water. When a planeswalkers named Jeska closed the last of the major rifts, it was as though the drain had been plugged. Dominaria's destruction was averted, the Multiverse was stabilized, and a new equilibrium reached between the spark and the Multiverse.

After this event, called "the Mending", the link between the spark and natural talent in magic remains, as does the potential to walk the planes. Planeswalkers now age normally, however, and although their spells protect them from far more harm than a normal being could endure, they can be wounded, and they can die. Planeswalkers must eat, drink, breathe, and sleep. They cannot inherently change shape at will, and they must draw mana from the land like any mage.

Planeswalkers remain much, much more powerful than mundane mages, however. Their connection to the æther makes them savants of sorcery. Their access to mana is not limitless, but because they can move across the planes, they can tap into the mana of lands their mundane counterparts will never see. Biological needs such as food and sleep can be fulfilled or eliminated with powerful spells. And although they age, some planeswalkers have mastered magic that slows or even halts their aging.

Above all, the planeswalker's arsenal of spells dwarfs that of the average mundane mage. Although nonplaneswalking archmages can achieve great power, over time a planeswalker's explorations of the Multiverse will result in a far greater breadth of magical knowledge.

Planeswalking
Think of planeswalking as the most difficult spell a planeswalker knows—the one that never gets easier. No longer can a planeswalker blink like Jeannie and find themselves on another plane. The act of planeswalking requires full concentration and no small amount of mana.

The act itself differs from planeswalker to planeswalker, because each planeswalker's identity is an essential part of the ability. For one planeswalker, a shamanistic ritual must be performed. For another, planeswalking is the culmination of a long, dreamlike trance. The details of a given planeswalker's method are dependent on who they are, how much of the Multiverse they have seen, and perhaps most importantly, what color(s) of mana they can wield.