Panda Cub: how to get the pet in WoW Forever
Panda Cub is a companion pet from Classic that returns in World of Warcraft: Forever. You learn it from one of these items: 
Panda Collar, 
Panda Collar and Panda Collar.
In short
| Item | Panda Collar, Panda Collar, Panda Collar |
| Source | Edition: Skyborne Epic Pack, Warcraft Forever Collection |
| New in Forever | no, from Classic |
| Account-wide | yes, according to Wowhead |
How to get it
Panda Collar comes with the Skyborne Epic Pack and the Warcraft Forever Collection, two of the digital editions of WoW Forever in the Battle.net Shop. It works only in Forever. What each edition contains is on the WoW Forever page.
The old item of the Collector’s Edition from 2004, Panda Collar, is still in the files too. In Classic it was the reward of the quest Welcome! for owners of that edition.
A second item for the same pet is in the files, Panda Collar; where it comes from in Forever is not known.
What changed since Classic
The item now teaches the pet: it becomes a spell and no longer takes a spot in your bags. Summoning it is instant instead of a 1 second cast, with a cooldown of 1.5 seconds.
Wowhead’s database marks the pet as account-wide: learned once, it would be there for every character. Blizzard has not confirmed that itself.
More pets from the same source
Every pet of WoW Forever, with where it comes from, is in the pet guide.
Frequently asked questions
How do you get Panda Cub in WoW Forever?
Panda Collar comes with the Skyborne Epic Pack and the Warcraft Forever Collection, two of the digital editions of WoW Forever in the Battle.net Shop. It works only in Forever. What each edition contains is on the [WoW Forever page](/forever/).
Is Panda Cub new in WoW Forever?
No. Panda Cub was already in Classic and returns in WoW Forever.
Sources: Wowhead