Planeswalkers
          
            Planeswalkers represent specific figures in the story of Magic: the
            Gathering. In this fantasy setting, the universe is actually a
            multiverse consisting of many dimensions called "planes", which
            planeswalkers have the unique ability to travel between (all other
            creatures being stuck in their plane of origin). Indeed, in the lore
            of the game, the players are planeswalkers themselves, channelling
            powerful magic to summon creatures, conjure enchantments, and so on.
            A planeswalker card, then, represents a "fellow" planeswalker whom
            you call to your aid. Despite the fact that planeswalker characters
            are living intelligent beings (humans, elves, &c), planeswalker
            cards do not count as creatures in the game rules. As
            counterintuitive as this is, perhaps a good interpretation is that
            they are "above the common rabble"; they have "agreed to help you
            out", but will not participate in such "low" activities as attacking
            your opponent directly. However, they do offer their services in the
            form of their loyalty. When you play a planeswalker, they enter the
            battlefield with some initial loyalty (shown in the bottom-right of
            the card). Once on each of your turns, you may activate one of their
            loyalty abilities; these will increase or decrease their loyalty by
            the stated amount. A "minus" ability can't be used unless the
            planeswalker actually has at least that much loyalty. Planeswalker
            abilities are as varied and diverse as those of artifacts and
            enchantments; they are often very beneficial, making planeswalkers a
            high-priority target for your opponent. A planeswalker's loyalty is
            decreased if they take damage; in keeping with the game's lore, if
            you control a planeswalker, your opponent may choose for some of
            their creatures to attack at your planeswalker instead of you. You
            may declare blockers accordingly; if a planeswalker ends up being
            damaged, their loyalty is reduced by that amount, similar to your
            own life.