520% run speed

First, go kill Pengsong for Tuft of Yak Fur 
Then go to Timeless isle and farm Windfeather Plume  from the elite birds

Now have a friend invite you to X-realm

Use the Windfeather Plume and Tuft of Yak Fur and once the mount is about to run out (~1sec left) either join the X-realm group or leave it.


Have fun running around with 520% run speed, you're able to cast and do whatever you want (more or less)

Any movement speed update/change removes it, aka you cant shapeshift, use stampeding roar or get dazed or slowed by mobs / players. Swimming works just fine as well as teleporting / Hearthstoning as long as you're not in inside places (removes the Windfeather Plume, without it speed is 440% and you're able to run inside houses etc too)