Yep. It's a combination of three mutagens, although one is not mentioned in the description.

Why are you farming for Madness? Are you aiming for a build like aimlessgun's? :P

I been 'farming' abit in Flotsam but i managed to get only one MADNESS mutagen. Can't really remember it's stats but it wasn't really impressive.

Where's the best place and monsters to farm for these mutagens? Harpies? Drowners? Nekkers? Endreagas?

I suspect anywhere that has monsters in large numbers ...
Nekkers probably, as there are spots where they spawn in swarms.

I received 2 madness mutagens in one of the Nekkar caves near Flotsam in act 1 and then never again during that playthrough. That's with patch 1.2 installed from the start of that run.

Who said I'm farming? I just wanted to see and hold one of those in my hands for once. Haven't had one my entire first playthrough.
My build... since my first on was almost exclusively magic, I'm now leaning towards swords/alchemy.

Just had one drop off an Endrega in ch 1. Haven't seen one pop out of alchemy yet though.

I just finished an Alchemy/Sword playthrough from aimlessgun's build and instead of going with the health and potion duration I went with bomb damage and change to get mutagen out of alchemy and I can say that I managed to get ahold of 7 Greater Power ones which skyrocketed my damage.

Nice. Definitely better than farming for mutagen.

Yes, I have gotten the whole spectrum so far, just no madness procs. I am pretty certain though that it's just a rare occurrence. Endrega's are my lucky charm so far, had another madness drop tonight.

I've found several in flotsam, yeah they are rare. Nekker Caves, Endrega Queen's, I think I've seen it drop on the Rotfiend guarding that herb. First playthru I only found 1, current playthru I've already found 4 and I'm at the conspiracy quest climax in ch2. I really don't think its the best mutagen(only 4 armor/15 vit with 2/2 impreg), nor that greater strength one that gives +1 vit regen(consensus is out of combat only?), I'd love the range if it did more than 2 signs and included bombs and thrown, the most uncommon for me has been the adrenaline one or signs damage, but I think the offensive crits has the greatest benefit.

I don't bother slotting mutagens til I hit 25 if I'm going with the impregnation in alchemy, think the next play throughs I think I'll go with only one branch just to see how differently specializing in one field changes the gameplay.

I found a Madness mutagen in flotsam; never actually used it though. It as +2 armor and some added vitality and that's it. If it had more shit, but eh. Does it have random properties or something? Does my next madness mutagen have entirely different added stats?

There are only two things that affect mutagen that I'm aware of, the degree, whether its lesser, normal or greater, AND impregnation, which increases mutagens by a %. IE the madness mutagen, I've never seen a lesser or greater, has 2 armor +5 vitality, with 1 in impregnation I think it goes to 3/10, and with 2 in it the madness then has a 4 / 15 i think
However impregnation only applies to those mutagens slotted after spending the point(s) in impregnation. I.E if you slot madness before impregnation, madness will still only give the base stats, however applying the mutagen after learning impregnation will slot the adjusted. You can see the increases in the inventory as they will also change once you have learned Impreg.

I've now crafted a madness mutagen (VERY expensive, don't try this at home). I wanted to know if it is true that it affects more stats than it states. And it is.

With impregnation 2/2 I get:
15 Vitality
+4 damage reduction (armor)
+3 min. damage
+5 max. damage