Out of the many ways that Witcher 3 offers you to empower Geralt, one of the most potent are mutagens, items that allow you to massively enhance your own combat-focused abilities. We'll show you where to farm red mutagens in particular as efficiently as possible.
Where to Get Red Mutagens
Unfortunately there's no enemies who can be guaranteed to drop these mutagens, but some are more prone to doing so than others. Bosses in particular tend to drop them when killed, but they almost never respawn, and therefore farming them isn't really an option after that first kill. Still, we found that Dead Drowned and Arachas were slightly more prevalent than most, and that Nekkers were a close second.
How to Farm Red Mutagens
Two known farming methods for red mutagens have arisen since Witcher 3 was released, one involving killing a Fiend in Crookback Bog, and the other involving hunting Drowned Dead along the coasts of Skellige.
However, the Fiend has since been patched out of the game, meaning that players who wish to farm should use the Drowned Dead method. To do so, fast travel to the Whale Graveyard in Skellige, across the island from Kaer Trolde.
Once there, you'll immediately be attacked by Drowned Dead, essentially just more powerful versions of Drowners. Use Igni to hold them back and put Necrophage Oil on your sword for added damage. There are two groups, one by the Signpost, and another some way up the coast by the broken wreck of a boat. Kill all of them and loot their bodies. They drop all kinds of lesser mutagens, including red ones. It's not guaranteed, but we found you could get one or two lesser red mutagens each time. Once they're all dead, find a place some way off to meditate and skip time forward for at least two days, or fast travel to a different region and back. The Drowned Dead should've respawned, allowing you to farm them all over again.
How to Craft Red Mutagens
The alternative is to craft your own mutagens in the alchemy menu, though you can only do this with the Blood and Wine DLC. By going to the merchant in Hauteville, Toussaint, players can buy formulas that show how to turn other green and blue mutagens into red ones. These both require the Rubedo ingredient as well as Winter Cherries, but even knowing what's needed, you'll still have to buy the formula to be able to make them.
Of course, while you're in the farming mindset, you can always check our guide here to farming gold. Alternatively, go to our guide on adrenaline and special attacks to boost your combat prowess even more.