Wolf Link is the legendary twilit beast form of the hero Link™. He first appeared in the Legend of Zelda™: Twilight Princess game, where he worked with the mysterious and mischievous imp Midna™ to take down a usurper to the throne, and to save Hyrule and the Twilight Realm from darkness.
Exclusive: Summons Wolf Link each time it's scanned - unless he runs out of hearts. Then you'll have to wait until the next day to bring him back again.
You can level up his hearts in the Twilight Princess game on the Wii U, then bring him into Breath of the Wild.