In Phase 3 of TBC Classic, the opening of The Black Temple and Mount Hyjal brings in seven Demon bosses. Because of this, physical DPS players' best consumable for those encounters will be the Classic Elixir: Elixir Of Demonslaying.
Because of the high demand for this Elixir, the price for these consumables will spike come Phase 3 (as they already have now). However, don’t be fooled or stressed; it is VERY easy to craft these, and in this guide, we’ll show you the best place to farm the materials to make these for yourself and your friends!
Ghost Mushrooms
One of the herbs needed to make these Elixirs is Ghost Mushroom. These mushrooms are typically found in caves in the upper level 40 areas. Popular places will be Skulk Rock and Jintha’Alor in the Hinterlands, Fungal Rock in Un’Goro Crater, and there’s even a spot in Zangarmarsh, in the Funggor Cavern. It’s no shock that places that have “fungus” in their name would be common spots to farm Ghost Mushrooms.
Hinterlands
The best locations in the Hinterlands are near Skulk Rock and Jintha'Alor, as shown below.

Un'Goro Crater
In the Un'Goro Crater, head through into the cave at the north-eastern edge of the map.

Zangarmarsh
The best farming spot in Zangarmarsh is down south, again in a cave.

Gromsblood
Gromsblood is the second herb needed to craft these Demonslaying Elixirs. Where Ghost Mushrooms spawned around caverns and fungal areas, Gromsblood spawns around demonic areas. The best spots to farm these will be in the Blasted Lands and Felwood. Two other spots, however, shine at some lower-level areas, being the Mannoroc Cavern in Desolace and Felfire Hill in Ashenvale!
Blasted Lands
Gromsblood spawns all around the Blasted Lands, as you can see in the image below.

Felwood
Again, you'll find Gromsblood all over Felwood, other than in the center of the map.

Ashenvale/Desolace
Both Ashenvale and Desolace have small clusters of Gromsblood, as shown in the image below.

Tip: GatherMate2 is a great addon for tracking where nodes are throughout the world. Once you hover over a node, it'll place it on your map/minimap similar to how we've shown it here in this article

The Best Spot for BOTH Herbs
Although these are great spots for both Gromsblood and Ghost Mushrooms, the BEST farm spot will be completely uncontested and free, because it's instanced! Dire Maul East contains around 4-5 Ghost Mushroom nodes and 2-3 Gromsblood. Players can herb these 5 times in an hour before getting the instance lockout, and in those 5 times, you should have enough mats for a couple weeks' worth of Demonslaying Elixirs!
Pusillins Room
This first spot is located where Pusillin will finally stop running away from you.

This next spot is directly above; just take the ramp up, and you'll see it

Hydrospawns Room
These next spots for both Ghost Mushroom and Gromsblood are in the room of the elemental boss, Hydrospawn.

Although Dire Maul East "Jump Runs" were very popular in Vanilla Classic, because of how high in demand Elixir Of Demonslaying will be in TBC, this is still one of the best instanced farm runs for Herbalists in the game! Since we are also now ten levels higher than we were in Vanilla, it is incredibly easy to avoid aggroing mobs throughout this dungeon!

Note: These herbs will not always be in the same spots but will typically always be in the same rooms!

First Gromsblood spotting by some Demons...
Old Ironbark's Hall
The final spot will be in Old Ironbark's hallway, where you can find your last Grombslood!

Elixir Of Demonslaying will be in very high demand in Phase 3 of TBC Classic on the Anniversary servers. If you have an Herbalist character or have guild mates who are, this will be an incredible farm for either personal consumption, gold farming, or stocking up for the guild bank!