Puscilla

When you look at the map, you'll see 3 bridges. It is the bridge that is pointing north that you want to go on. You will see a small cave entrance with tons of imps inside. Go all the way into it, Puscilla is up at the top inside the cave.

The location of the world quest marker is deceiving. It is not in the cave that you get to by going right out of the Veiled Den transport point. It is above that cave and requires you to run to the spoke with the 3 pathways and taking the rightmost pathway into a cave (where you'll dismount). Puscilla is not the imp mother you first see in the cave (you can ignore that one and just run past). She is all the way at the top (take a right when there is a left and a right option).

The rares who drop these mounts only yield loot for you once per day. I have created a macro to track whether they have been killed by you during this reset:

/run for k,v in pairs({Hound=48821,Blistermaw=49183,Vraxthul=48810,Puscilla=48809,Skreeg=48721,Wrangler=48695}) do print(format("%s: %s", k, C_QuestLog.IsQuestFlaggedCompleted(v) and "\124cFFFF0000Completed\124r" or "\124cFF00FF00Not Completed\124r")) end

The macro tracks the following rares (since they drop similar mounts):

[npc=127288] who drops [item=152790] found in Antoran Wastes at 63.1 25.3
Blistermaw who drops [item=152905] found in Antoran Wastes at 61.8 37.3
[npc=126199] who drops [item=152903] found in Antoran Wastes at 53.2 35.8
Puscilla who also drops [item=152903] found in Antoran Wastes at 65.5 26.7
[npc=126912] who drops [item=152904] found in Eredath at 49.6 10.0
[npc=126852] who drops [item=152814] found in Eredath at 55.7 59.8