Ambergris
From Discworld MUD Wiki
Ambergris can be used to purchase special items sold in Niknax's shop.
After you complete every few SS Unsinkable sailing missions from Chidder, when you collect payment
you will get some amount of ambergris.
a piece of white ambergris This is a piece of ambergris, a rare waxy mineral found on beaches that's prized for its sweet, musky smell. The paler the ambergris, the better its fragrance - this small marbled white lump is worth a great deal to the right people.
Ambergris is a continuous item, which means they stack and only count as one item even if you have lots.
Four pieces of white ambergris weighs 1 g.