Millennial Jade Deer

Millennial Jade Deer is a Legendary Pet that was released alongside Millennial Tree Cookie's Magic Candy in the second half of the Long Journey for Life update. It passively slows Energy drain and transforms into a Millennial Beast which marches in front of the running Cookie, covering holes and leaving behind Sacred Forest Jellies.

Story
''One day, the pure energy of a forest so deep nary a Cookie ever dared traverse it, gathered and took shape of a giant deer spirit. Millennia passed with this monstrous guardian roaming the woods, safekeeping the life residing within from outside threats. Not even when Millennial Tree Cookie approached did the deer lower its guard, until the Cookie helped the nearby Grass Village flourish and grow ever verdant. As long as this towering warden remains, so shall new seeds grow and blossoms sprout evermore.''

Trivia

 * The Millennial Jade Deer’s design and/or story may be a reference to the Forest Spirit from the Studio Ghibli film Princess Mononoke.
 * Millennial Jade Deer's internal name is "pet0125".