Caustic Muck

Caustic Muck is primarily found in Revendreth. It can be...
 * Purchased for from Au'larrynar in Maldraxxus;
 * Purchased for from Dirk, Gobbers, and Muckfist in Revendreth;
 * Looted from Pugilist's Prizes and Hopebreaker's Packs in Revendreth;
 * Or dropped by the Amalgamation of Filth and the Bog Beast in Revendreth.