Mutagens are useful colour-coded cells that can be acquired from slain monsters and are used to boost Geralt‘s powers. Not every dead monster will drop one, but they’re worth collecting when they do.
Red Mutagens in particular are quite useful because they boost your attack power, but finding enough of them to use in your experiments can be a frustrating, time-consuming process.
The best monsters to “farm” to get more red mutagens are:
Drowned Dead and Necrophages
Although at the start of the game it will be a while, probably, before you see your first red mutagen. They are extremely rare to begin with, but seem to become more prevalent the higher level you become.
The first red mutagen I got in my last playthrough appeared at level 15 and came from The Apiarian Phantom. In previous playthroughs I’ve gotten red mutagens sooner, from generic monsters. There’s obviously an element of luck involved.
During the early part of the game your best bet for getting hold of red mutagens are Drowned Dead on Skellige. There are two places where these monsters regularly re-spawn and are worth visiting to try to get red mutagens: the Whale Graveyard, and Redgill – both found on the east coast of the main island, Ard Skellig.
What I do is: fast travel to the Whale Graveyard; kill the Drowned Dead; take their mutagens; then jump on Roach and ride to Redgill. Over the hill, just past Redgill, is a beach where you’ll always find four or five Drowned Dead – ripe for mutagen farming. Here’s a video of the process.
There are a few things to note about this plan, though. Firstly, at the Whale Graveyard – before you get Drowned Dead spawning there – you’ll find a bandit camp that is actually associated with the level 15 quest “The Family Blade“. You’ll have to clear that first before the Drowned Dead start appearing. Secondly: on the path to Redgill you’ll encounter a level 30 Cyclops, guarding some treasure, and you’d be well advised to run or gallop straight past it. You’ll also encounter two separate groups of Harpies too, but just gallop past all of them on Roach.
If you keep returning to the Whale Graveyard every now and then, and galloping to Redgill, you’ll build up your store of red mutagens quite quickly.
Oh, and DON’T turn all of your lesser red mutagens into regular or greater red mutagens. You need some lesser red mutagens for other things! Only convert the mutagens you need.
High-levelled Endregas can also be a good source of red mutagens. They seem to re-spawn quickly too, so if you find a large nest (there are quite a few on Skellige and in Velen/Novigrad) you can pick them off fairly regularly and make a good income on mutagens.
When you complete Blood and Wine, you’re given a device called Mutagenator by Regis. What this does is generate extra Greater Mutagens by counting 100 monster kills as a single “charge”. Once it’s charged up with 100 kills, a message then tells you it’s active. Use it when it’s active and it will give you one red, green or blue Greater Mutagen. You then have to charge it up again. The colour Mutagen it gives you at first is random, but once started it tends to dispense them in cycles.
The Witcher 3 Guide 