TheWoWDBNow confirmed it is indeed from an achievement, which is: Vale of Eternal Blossoms
Spell
Astral Emperor's Serpent
Physical
The highest voted Wowhead comments for this page. They are community notes, not TheWoWDB comments.
Tooltip
Summons and dismisses this mount.
Spell facts
SchoolPhysical
Cast time1.5 sec
DurationInfinite
EffectApply Aura
RangeSelf Only
Taught byMounts (skill 1)
Spell ID446022
Datamined from the current retail build. Numbers that scale with level or stats are shown at their base value.
Items that grant this spell
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Community notes from Wowhead · 2 comments
Top 1 shown above · 1 more hereThe comments below were written by Wowhead users. They are community notes, not TheWoWDB comments. See them in context on Wowhead.
This golden version of the Astral Cloud Serpeant and many other mounts (32 in total) were added to the PTR 10.2.7 patch for the upcoming "Timerunning: Pandamonium" special event.
Likely a drop from Elegon within the Mogu'shan Vaults raid (when accessed during the special event queues), much like the Astral Cloud Serpeant, or possibly even awarded via an achievement associated with the event.