Novigrad Hospitality is a short secondary quest that can be picked-up while riding through Yantra. Two men, Victor and Gascoigne, invite Geralt over for a drink, then try to steal his things.
Gaunter O’Dimm, aka Master Mirror, is clearly an allegory for “the devil”. Or some sort of malevolent demon. Whoever he really is, the fact is: he’s a sinister man.
To find this re-spawning, level 20 Cockatrice: draw a line directly north from Oxenfurt Gate in Novigrad, and draw a line directly west from Yantra, and where they meet is where you’ll find it.