What does it mean to planeswalk?

Planeswalking refers to the act of moving from one plane of existence to another within the context of Magic: The Gathering lore and gameplay. In the game, this is often represented through the use of plane cards, which can depict different worlds or settings from the Magic multiverse. When a player planeswalks, they are essentially transitioning to a new environment that alters how certain spells, abilities, and interactions work during the game.

The correct choice is the one that involves putting the face-up plane card on top of the planar deck. This reflects the act of transitioning to a new plane, which is integral to the narrative and mechanics surrounding planeswalkers—powerful individuals capable of traversing the multiverse. By placing the plane card on top, players can clearly signify which plane they are currently inhabiting, as each plane can have unique rules or effects that may influence gameplay.

Other choices describe actions that either do not directly relate to the concept of planeswalking or focus on mechanics unrelated to moving between planes within the game. Hence, the correct answer accurately encapsulates the mechanics and thematic context associated with planeswalking.