Airborne Tumbler

Spot I used to farm this, was "How to Train Your Protodrake" world quest. Lots of players in a small area using their dragons to carry protodrakes to the quest spot. Pretty easy to park on a cliff and dive in for the dismount.

I had problems with the How to Train Your Dragon world quest area as the movement of players is mostly unpredictable, so I searched and found that Sulfur Wastes in Zaralek Caverns are packed with bots farming herbs and ore near the lava river. You can easily stalk them and hit them when they are in place after they mount up and lift off. About 40 dismounts in less than an hour. As a bonus you can report the bots and kill them. Beware of the one botting character who will, after a while, switch into full human mode and who will start to hunt you. I surely had fun!

With the addition of Soar (one of the Dracthyr racial abilities) gaining the full effects of Dragonriding/Dynamic Flight in 10.2.5, you can now complete this achievement as a Dracthyr in your base dragon form.

If you use Whirling Surge while using Soar in War Mode, you will dismount enemy players, and receive credit towards the achievement.