Sinrunner Blanchy

To get Sinrunner Blanchy you have to bring items to [npc=173468] 6 times in Revendreth.
You can do it only once per day (daily quest reset) so you need 6 days to get the mount.
You can obtain all the items you need in advance.
[npc=173468] spawns on the river in Endmire north of Darkhaven
and starts to run until it bumps into a player. Everyone can interact with it.
It despawns after 5 minutes. The respawn timer is from 1 to 2 hours.
/way 63.13 43.11 Dead Blanchy Spawn
Full Guide: https://youtu.be/eAZsE0owI8A

Day

Items to bring

Location

Video

1

[item=182581] x8

In [object=2724] north part of Westfall Eastern Kingdoms

https://youtu.be/FhoC7dJlJbY

2

[item=182585] x1

Speak with [npc=173570] in Darkhaven.

https://youtu.be/Xd6Si8DNlFQ

3

[item=182595] x4

[object=357541] on the roads north and east of Darkhaven.

https://youtu.be/QEd83yjEl4M

4

[item=182599] x1

[item=182620] in Darkhaven, near the carriage. Fill in Ardenweald or Bastion.

https://youtu.be/b2sJnx8akdE

5

[item=182597] x1

[npc=171808] south of Wanecrypt Hill flight point in The Night Market. Sold for random meat x30.

https://youtu.be/sHBmVHjRlJc

6

[item=179271] x3

[npc=167815] northeast of Charred Ramparts flight point in Hole in the Wall.

https://youtu.be/UzhWd2cNFuk

Each time you give the item to [npc=173468] it will react with the following emote:
Meet Blanchy first time -> Dead Blanchy's eyes are frenzied. Her form is sickly and gaunt.
She is clearly famished and needs a hearty meal.
Handful of Oats -> Dead Blanchy accepts the oats enthusiastically. Though she is shaggy in patches,
her skin ripples with irritation from stinging mites, sharp thorns, and smelly muck.
Grooming Brush -> Dead Blanchy shivers and nuzzles you as the grooming brush cleans the irritants from her skin.
As she shifts her weight and stamps, you notice her hooves are badly chipped.
Sturdy Horseshoes -> Dead Blanchy lifts her hooves obediently, happy to save her injured feet tended.
She's out of breath and blowing hard and seems very thirsty.
Bucket of Clean Water -> Dead Blanchy eagerly drinks the entire bucket before butting her head against you.
She's quenched her thirst but is shivering uncontrollably.
Comfortable Saddle Blanket -> Dead Blanchy stands very still as the saddle blanket is placed upon her.
As her shivering slows and then stops, Blanchy begins searching your bags for a treat.
Dredhollow Apples -> Dead Blanchy's nostrils flare as she scents the apples. She eagerly crunches them up.
Dead Blanchy sights contentedly and places her head on your shoulder.

TomTom coordinates:
In Westfall:
/way 55.14 27.42 Oats (Day 1)
/way 56.26 30.17 Oats (Day 1)
/way 52.16 33.56 Oats (Day 1)
/way 51.02 39.08 Oats (Day 1)
/way 46.57 37.79 Oats (Day 1)

In Revendreth:
/way 63.13 43.11 Dead Blanchy location
/way 63.39 61.75 Grooming Brush Snickersnee (Day 2)
/way 70.33 59.05 Horseshoe (Day 3)
/way 74.52 57.84 Horseshoe (Day 3)
/way 64.22 58.42 Horseshoe (Day 3)
/way 65.18 74.11 Horseshoe (Day 3)
/way 68.14 68.86 Horseshoe (Day 3)
/way 61.28 69.41 Horseshoe (Day 3)
/way 63.20 65.72 Horseshoe (Day 3)
/way 63.32 61.59 Empty Water Bucket (Day 4)
/way 51.13 78.80 Comfortable Saddle Blanket Ta'tru (Day 5)
/way 40.85 46.67 Dredhollow Apple Mims (Day 6)

In Ardenweald:
/way 53.17 35.11 Fill Water Bucket (Day 4)

I tried something out that I thought Blizzard might have implemented. Turns out they did!
I took Blanchy back to their previous life.

Spoiler

If you are mounted on Sinrunner Blanchy when you get close to the scene of the death of Old Blanchy, you automatically dismount and get the text "Sinrunner Blanchy screams in anguish and then fades from view.". Seems to have a cooldown as I could only get it to happen once every few minutes or so. Torturing Blanchy for science.

Finally, Old blanchy is in our care.