Under what circumstances can a player planeswalk?

The correct understanding of planeswalking pertains specifically to the context of Planar Magic, which is a variant format of Magic: The Gathering. In Planar Magic, players interact with a specific deck of plane cards that add unique effects and themes to the game, allowing players to "planeswalk" from one plane to another as part of the game's mechanics.

In this format, planeswalking occurs when certain conditions fulfilled by the game state allow players to transition to another plane, gaining access to the features and rules applicable to that new plane. This action fits seamlessly within the context of the Planar Magic gameplay, as it is designed precisely for exploring different planes within the game's multiverse.

For other game formats, planeswalking does not occur; players can only engage with the game through the rules and mechanics established by the format they are playing. Therefore, while elements of planeswalking are conceptually present, the actual action of moving between planes is confined to the Planar Magic format and does not apply in standard gameplay or other variations of the game.