Primal Shadow comes from motes of Shadow. These drop in just about every zone from Voidwalkers mainly. Some people have reported them from other demon / infernal type mobs but we will stick with Voidwalkers for this guide. The good news is if you are mid 60's there are a lot of locations you can farm in Hellfire Peninsula and it's actually the highest drop rate reported, near 30%. The very far southeastern strip of Hellfire Peninsula is loaded with void walkers, if you go east over the mountain from Zeth'gor you'll find it. There is also a spot in Nagrand killing Voidspawns (64-66) that has a 23% drop rate, just run circles around Oshu'Gun and you'll see what I mean. Here is a list of instances that has Voidwalkers in them that you can also get a few motes from if you're grouping.
- The Arcatraz - Tempest Keep - Negaton Warp-Master/Screamer 50-93% drop rate, depending on dungeon difficulty
- Mana-Tombs - Auchindoun - Nexus Terror 29% drop rate
- Both of those instances have bossesin them that can drop motes as well
The southeastern coastline of Hellfire Peninsula is reportedly the best but if you're also looking to get some higher level items to sell then you will want to head into Netherstorm where the drop rate is just slightly behind Hellfire Peninsula for motes of shadow. Check the map to find the location.