Planeswalkers are powerful beings in the Magic: The Gathering universe who can travel between different worlds, known as planes. They possess unique abilities and spells, allowing them to manipulate the game's mechanics and influence battles. In gameplay, players can use Planeswalker cards to summon these characters, each with their own set of abilities. They often serve as allies in a player's strategy, providing additional resources and effects that can turn the tide of a match.