Shadow (companion)

Shadow is a fox companion that will periodically change color from Light to Shadow.

Source
This item is available from the shop or the In-Game Store for $10 or €10. It was released on September 12, 2017.

Pet Journal
Lost on Argus and overtaken by darkness, this playful fox can shrug off the void just by being by your side.

This little fox is shrouded in shadow, but has a heart of gold.
 * In-Game Store

The Foxiest Pet in Your Collection - ''Lost on Argus and overtaken by darkness, this playful fox can shrug off the void just by being by your side. With its adorably oversized ears, it'll be at your side, trotting through every battle. At the end of the day, curl up next to this cuddly canidae and admire its color-changing coat with its light and shadow effects. It's yours to keep.''
 * Blizzard Shop

Trivia

 * Between September 12 and December 31, 2017, Blizzard donated 100% of all USD sales of this pet and the plush to the and the, with donations split equally between both organizations. Over $1.8 million dollars was raised.
 * Shadow was originally planned to be released during BlizzCon 2017, but due to the two Atlantic hurricanes and, flooding in South Asia, and various other natural disasters, Blizzard made the decision to release the pet early on September 12.
 * An official Shadow plush, featuring a light-up rune and poseable ears, is available from the Blizzard Gear store. Between November 9 and December 31, 2017, much like with the in-game pet, Blizzard donated $18.00 USD of each plush sale to to the American Red Cross and the International Federation of Red Cross and Red Crescent Societies, with donations split equally between both organizations.
 * Shadow's appearance is based on that of the (Vulpes zerda), a species of small fox native to the Sahara desert that is notable for its unusually large ears.