I was going for the Sundancer mount the other day and I bought the Skystrider Glider off the AH, got the shrine blessing, used the glider and mounted Sundancer. Got him landed, killed him, and didn’t receive the mount. When I put in a ticket, because I thought the person that landed him was guaranteed the mount, I get the following response:
This is Game Master Valaladur here to help you with your concerns in being unable to receive the Sundancer mount. Thanks for reaching out to me so that I could help look into this for you.
I can absolutely understand your concerns in this situation, especially when it would feel like something would just simply be not appearing to work.
In this situation when it comes to earning this mount, there are quite a few things that can cause you not to get this mount. The having the achievement earned wouldn’t provide you the mount and this mount is looted directly from the corpse of this NPC. As this is still considered a “secret”, going into details about obtaining this mount is not something that we would be able to share.
There was previously an issue that was preventing individuals from being able to loot this mount, however it has since been fixed by the developers, but this fix was not retroactive as we are unable to verify the full eligibility requirements of this mount and thus would mean we would not be able to grant the mount or provide any replacements of items used to attempt in obtaining this. You would need to get with a friend or someone else to help in obtaining this again if you needed a new glider.
If you need help with anything else, or just a question, please do reach back out! Farewell and have a great rest of your afternoon! 
I need to know if the mount is supposed to be 100% drop for the person that lands Sundancer and your GM also needs to know that the loot is NEVER looted off of Sundancer’s corpse ever. He bows, and disappears and the loot goes in your bags automatically.