Swift Gloomhoof

The ballads of Ardenweald claim that the birth of gloomrunner heralds the passing of a particularly benevolent wild god. Seeing a gloomrunner is therefore a blessing and a curse.

Riding Requirements:

This mount is available to all eligible characters on your account.
Level 10
Apprentice Riding (ground)
Expert Riding (flying)

Source:

Night Mare in Dreamshrine Basin, Ardenweald.

Notes:

The Night Mare that drops this mount isn't normally visible, instead you need to use a Dream Catcher and be level 60 in order to see it:

First, head to Tirna Scithe, which is the peninsula on the south-west edge of the zone, connected by a narrow land bridge. Head around the north of the zone, to roughly the north-west corner (18, 62). If Oranomonas is the world boss this week they'll be in a different clearing just to thr south of this one. Here you should see a tree hanging off the edge of the world, with roots hanging down.
This is the most difficult part: you need to get from the edge of the world over to the narrower winding root. It's apparently possible to jump this on a mount, but you may fail and fall. Hunters can disengage over, Venthyr can use Door of Shadows. Or you can simply use a Goblin Glider Kit.
Jump to the adjacent broader tree root, and follow it up to the base of the tree. The cross a tree root bridge back to the mainland. Carefully circle to the left around the base of the enormous tree, until you come to a cart. Click on the Cracked Soulweb at the front of the cart, on the ground. You'll now have a Broken Soulweb.
For the next stage, you must have (i) 10 pieces of Lightless Silk, and (ii) completed two quest chains: Trouble at the Gormling Corral and Tricky Spriggans. Neither chain is directly tied to this mount, but unfortunately you can't speak to Elder Gwenna at Glitterfall Basin until they're done.
Ensure 10 pieces of Lightless Silk are in your inventory, then head to Glitterfall Basin and speak to Elder Gwenna. If she's present she'll be north-west of the flight point, on the other side of the camp, by Aldas, the General Goods vendor. Select her dialogue to receive a Repaired Soulweb.
To enchant your soulweb you need to speak to Ysera in the Heart of the Forest. If you're in the Night Fae Covenant you can simply enter and speak to her directly. If not then you can speak to an Elite Queensguard at the entrance and they'll summon her out to you.
Speak to Ysera and you'll receive your Dream Catcher.
Head to Dreamshrine Basin, which spans an arc north, east and south of the Hibernal Hollow flight point.
Activate the Dreamcatcher. This is a permanent item and you can use it as often as you want, so you don't have to worry that you might waste it. It'll give you a 5-minute buff and put you into a special phase where you can see the Night Mare. If it's currently up it'll path around the area, otherwise you may have to wait half an hour or more for it to spawn.
You must defeat the Night Mare to receive the mount. Theis can be a very difficult fight to solo unless you're well geared, but you can receive help from other players who have the Dreamcatcher. Be sure to interrupt its Cosmic Shower ability, and run out of range when it casts Total Eclipse. Good luck!