The Glacial Tidestorm is guaranteed to drop twice off mythic Jaina in Battle for Dazar’alor, which is fairly easy to do with people who follow some simple directions. Mooglegem got the drop on her first try when I showed her the strat. Here she is with her Glacial Tidestorm, Squishy (her water elemental), and Aborius, the elemental fury in Nagrand!
It took me a lot more runs, but I got mine too! I got on my frost mage for the screenshot so we could have maximum water elementals!
We had to visit alternate Draenor as well of course!