Zergling: how to get the pet in WoW Forever
Zergling is a companion pet from Classic that returns in World of Warcraft: Forever. You learn it from one of these items: 
Zergling Leash and 
Zergling Leash.
In short
| Item | Zergling Leash, Zergling Leash |
| Source | Edition: Skyborne Epic Pack, Warcraft Forever Collection |
| New in Forever | no, from Classic |
| Account-wide | yes, according to Wowhead |
How to get it
Zergling Leash 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, Zergling Leash, is still in the files too. In Classic it was the reward of the quest Welcome! for owners of that edition.
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 Zergling in WoW Forever?
Zergling Leash 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 Zergling new in WoW Forever?
No. Zergling was already in Classic and returns in WoW Forever.
Sources: Wowhead