When adventuring in Underworld a traveller may encounter some of the human pioneers who discovered the area. One of the first to be found is Gretchen the Alchemist.
Gretchen offers a very simple quest named ‘Curiosities’, fulfilling it requires you to provide some basic ingredients, and though she asks you to find them in underworld, they are far more readily discovered in the old lands or can even be purchased in the shops of the Royal City of Ter Mur.
On returning with the fertile dirt and bone samples she has asked for Gretchen will reward you with an exploding tar potion. 
The potion is thrown like an explosion potion and has a ‘forced walk’ effect, but can be resisted by players with high magic resist.