Voidglower
Source: Pet Battle. Is the void glow in addition to their natural glow, or does it replace it? The world may never know. Flying type. Macro for all the known spawn locations (make sure you are in the Vale when you use it!):
Voidglower is a wild Battle Pet found in the Titan Assault version of Vale of Eternal Blossoms, requiring completion of the Visions of N'Zoth questline before it becomes visible.
Guide awaiting review
Unlock the Correct Phase
You must complete the questline that introduces the Visions of N'Zoth invasions to Uldum and Vale of Eternal Blossoms. Without this, Voidglower and other patch 8.3 wild pets will be invisible to you regardless of where you search.
Travel to Vale of Eternal Blossoms
Head to the Titan Assault version of Vale of Eternal Blossoms — the assault does not need to be actively ongoing. Voidglowers typically appear in packs of three scattered around the zone. Check at 47.2, 31 and 57.4, 46.4 as starting search points.
Search Additional Spawn Locations
Continue searching at 38.6, 59.6 and at 27.6, 51.2 near Winterbough Glade at 26, 50 if you have not found a tamable Voidglower yet.
Force Tamable Spawns to Appear
If no tamable Voidglower appears, use a targeting macro cycling through Golden Chirper, Voidglower, and Voidskimmer to locate critter versions, then kill them. Clearing critter versions of pets across the zone frees up spawn slots, causing tamable Voidglowers to appear in their place.
Tips
There appears to be a cap on the total number of tamable pets allowed in the zone at one time — killing off non-battle critter versions throughout the zone is the most reliable way to trigger tamable Voidglower spawns.