Primal Stormling
Source: Quest. Raindrops whip around this creature with frightening speed, ripping and tearing anything that touches it. Experts say the best way to avoid injury ... Elemental type. Just a heads up: This pet is only available during Pre-Patch. However, it is cageable.
The 
Primal Stormling is a battle pet obtained during the Dragonflight pre-patch by completing the questline leading to 'A Primal Threat' or by purchasing it with event currency — and since it's cageable, it can also be found on the Auction House.
Guide awaiting review
Note Pre-Patch Availability
The Primal Stormling is only directly earnable or purchasable during the Dragonflight pre-patch event. However, because it is cageable, it can be bought from other players on the Auction House even after the event has ended.
Start the Questline
To unlock 'A Primal Threat', complete the following quests in order: The Dragon Isles Await, Aspectral Invitation, The Dark Talons / The Obsidian Warders, and then Expeditionary Coordination alongside Whispers on the Winds (these two are worked on at the same time). After finishing those, pick up 'A Primal Threat' from Khadgar.
Purchase from Event Vendor
Alternatively, you can purchase the Primal Stormling using event currency from Agni Blazehoof at 56, 39.4 in The Forbidden Reach. The vendor also sells the 
Elemental Potion of Power and other event items.
Tips
Quests 3 and 4 in the pre-patch chain — Expeditionary Coordination and Whispers on the Winds — are completed concurrently, so work on both at the same time to save time.
