Potency is the first part of this- the first ingreedient is found only in the fearsome creature known as a Mist Horror.  You are to find Mist Creepers in the swamps to the Northeast, and kill them until the Mist Horror appears.  Slaying the Mist Horror next, you need to bring him the heart of the plant-creature.

For the sake of the brew’s body, you need Pristine Crocolisk Eyes from the crocolisks in the same bog (convenient...).  You need five of the eyes in perfect condition, and that’s going to take a bit of doing- skinners will probably be very happy with this, though.

Finally, for the hue, or color, of the brew, he is goign to need 8 wings- wings from Glittering Amberflies, the creatures the nearby bog is named for (this is getting a bit beyond coincidental, leading to all manner of questions about the nature of the local bog...).  To this end, he gives you a knife to sever the wings from their corpses with.

The Amberflies are the simplest part of this- while they deal decent poison damage, the bugs aren’t aggressive nor are they terribly powerful.  In order to get the wings, you’ll need to kill eight of the creatures, using the knife on each corpse after looting it of anything valuable.  A touch annoying that the quest eats a slot in your inventory and needs to be enacted on each bug separately, but so it goes sometimes.

Crocolisks are second in difficulty here- while they are aggressive, large, and prone to wandering into other swamp denizens, their only real special attack is ‘gorge’, which is a slight increase in damage but not much else worth noting.  Sadly, their drop, the Pristine Crocolisk Eye, is not guaranteed at all like the wings from the Amberflies, so you’re going to have to see a lot more of them than of the Amberflies.

The Mist Creepers aren’t too much of a problem- while they are ugly cycloptic plant-giants, they aren’t too damaging or powerful in general, and are actually frailer than the crocolisks you can find here.  The Mist Horror is a little more difficult though- especially when you aren’t sure how to get it to appear.  Once you’ve killed enough Mist Creepers for the quest, you’re going to need to linger around the bog for a while.  Eventually, the screen will cloud around the edges with greenish-brown murk, and a small orb of ‘Inconspicuous Fog’ will appear behind you.  You’ll also gain a buff that declares ‘You’re being hunted...’ (Why this is a buff and not a debuff is beyond me).  In order to get the Mist Horror to appear, you’ll need to manipulate the ball of fog following you, rather than just waiting around.  This prompts the Mist Horror to appear- but it’s just an oversized and slightly more damaging Mist Creeper, so it’s not nearly the challenge you might be anticipating.

Killing the Mist Horror grants you the Mist Horror Heart, and clears out the mist from around you so you can see clearly again.