Planeswalkers: Planeswalkers who ignited Pre-Mending, Planeswalkers who ignited Post-Mending: A-M, N- Z Planes and their peoples: Factions, Other Characters (Dominaria, Phyrexia, Rath and Mirrodin), Planes
During the events of the "Time Spiral" block, Dominaria was on the verge of reality tearing apart and the plane being unmade (and since Dominaria is the hub of the Magic universe, all other planes would fall soon after), mostly due to the various apocalypses the plane has been subjected to throughout the eons. The storyline ended with the rifts healed, but at a price; many of the old-style Planeswalkers gave up their Sparks, or in some cases, their lives, to fix the problem. The nature of the Spark itself had changed as well. The odds of being born with (and igniting) the Spark were about the same, but new-style Planeswalkers aren't nearly as powerful; they're mortal, and can't planeswalk as easily as their predecessors (it usually involves a ritual of some sort). They can't create their own worlds or shapeshift on a whim anymore, either. They are, however, "weak" enough to be printed on Magic cards without destroying game balance, and are exclusively in the Mythic Rare rarity slot (with the exception of the Lorwyn blocknote and War of the Sparknote ).
These pages are for Planeswalkers whose spark ignited after The Mending took place, not just those who were introduced afterward. Despite their first appearance being years after the event in question, Planeswalkers like Nahiri and Ugin belong in the pre-Mending category.
NOTE: Spoilers up through the most recent set (as of now, Strixhaven: School of Mages) may be unmarked.