Sundancer

Travel to the small circular island at 60, 93 in Bastion and click the Ancient Memorial Monument, a floating abstract figure with wings. This grants you Sunrider's Blessing, a 30-minute buff required to start the acquisition chain.

While under the effects of Sunrider's Blessing, use a Skystrider Glider to glide. The moment your character model transforms into the Echo of Dresaelus, a hidden 5-minute buff is applied — note that this buff does not appear in your buff bar.

Glide onto Sundancer at 62.27, 81.14 in Bastion while the hidden Echo of Dresaelus buff is active. Be aware that Sundancer will deal damage to you while you ride it, and once it lands it becomes a combat encounter with 590,000 HP — bring friends to help kill it.

Sundancer must be defeated before the 5-minute Echo of Dresaelus timer expires to guarantee the mount drop. If the timer runs out before the kill, the guaranteed drop is lost. A goblin glider cannot be substituted for the Skystrider Glider — only the Skystrider Glider triggers the required buff.

If Sundancer is activated but not killed and despawns, the respawn timer is roughly 45 to 60 minutes.