Red mutagens are easily the most sought after in The Witcher 3 and if you are looking to get them in Velen, this is the most reliable way.
Farming red mutagens reliably is tricky in earlier levels of the game and stacking Geralt's attack power is rather minimal before you are able to craft greater red mutagens. That said, you will need a total of nine lesser red mutagens to get one greater and they drop rarely in the earlier parts of the game while you are still prowling Velen and Novigrad.
Well, there is one reliable way to get them, thanks to a respawning Alghoul in a village called Toderas but there are a few prerequisites you need to complete before the necrophage can be farmed. The village itself is located directly east of Crow's Perch and directly south of Oxenfurt. You can pinpoint its location by the intersect of the lines from these two points.
Getting Toderas Alghoul to spawn
First, you need to visit Toderas in order to witness or participate in an altercation between two groups of peasants with no morals.
Once they are all dead, you will need to depart the village, leaving you with two options:
- Fast travel to White Orchard and meditate for a few days
- Continue doing your work in Velen/Novigrad area for a while before returning
The exact details on the Alghoul's first spawn are a bit blurry but it will eventually come along after Geralt's initial encounter with peasants.
Farming the Alghoul for red mutagens
Once the Alghoul appears, it's pretty straightforward. It will be accompanied by several Devourers, who are more powerful versions of Rotfiends, but you don't need to kill them since it's only the Alghoul that can drop the red mutagens.
This can be repeated with the following steps for infinite red mutagens:
- Fast travel to Toderas and quicksave
- Kill any necrophages you attracted
- Loot the Alghoul for the red mutagen
- If it dropped a green or blue mutagen, reload the quicksave and kill it again until you get a red
- Fast travel to White Orchard
- Repeat the first step, rinse and repeat
Tips for farming the Alghoul faster
You can use a Devourer explosion to kill other enemies, including the Alghoul, in a single hit. Just be mindful that it doesn't catch you as you might die as well.
Make sure you are at least level 11 if you're playing on Death March difficulty. You will be able to get Griffin School swords at this point, making the combat much faster.
Use Quen if you are fighting Alghoul directly, without causing a Devourer explosion to kill it. The reason for this are the spikes the necrophage grows on its back. If you're not shielded, they will stagger you whenever you hit it with an attack, dragging the fight out.
That's about it, happy mutagen hunting!