A player has looted the Sha of Anger mount twice from a single world boss kill!
The first mount was looted from the Mists of Pandaria world boss. The second mount dropped from a bonus roll.
Blizzard increased the drop chance of select MoP and WoD mounts on live servers back in November 2022, but the odds of this happening are still quite slim.
Here’s a screenshot of the double Reins of the Heavenly Onyx Cloud Serpent drop.
Source: Reddit