212.9d.

Loyalty is a characteristic only planeswalkers have. The loyalty of a planeswalker not in play is equal to the number printed in its lower right corner. The loyalty of a planeswalker in play is equal to the number of loyalty counters on it. A planeswalker is treated as if its text box included, "This permanent comes into play with a number of loyalty counters on it equal to its printed loyalty number"; this ability creates a replacement effect (see rule 419.1). As a planeswalker gains or loses loyalty, loyalty counters are put on it or removed from it, respectively. Damage dealt to a planeswalker results in that many loyalty counters being removed from it. If a planeswalker's loyalty is 0, it's put into its owner's graveyard as a state-based effect. See rule 420.5.