This quest is not available in game.
Apothecary Faustin at Beggar's Haunt needs 5 Shadow Panther Hearts, Mire Lord Fungus and some Green Whelp Blood.
I have just the right serum in mind. It will deal with the truth in precisely the way the truth should be dealt with.
For this concoction I will need several Shadow Panther hearts from the Swamp. I also require the enchanted fungus off of the Mire Lord who resides there. I am sure one as able as you, <name>, can persuade him to part with some.
The last item I'll need for the serum is the blood of a dreaming whelp, like the ones that live outside Itharius' cave in the swamp.
Now, off you go!