Talk to the Voodoo Gentleman so that Don gets a robe. But the robe does not reak bad enough to fool the Fishmouthians. Talk to the VG until he mentions the robe should smell fish.
This is the low-spoiler guide for "Making the robe stink" puzzle in Gibbous - A Cthulhu Adventure. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.