Mercury

Mercury is one of the four magical resources in Heroes (along with Crystal, Gems and Sulfur). Mercury are needed for several buildings, recruiting Devils, Arch Devils, Ghost Dragons, Azure Dragons and Phoenixes. The primary source of Mercury is the Alchemist's Lab, which brings its owner 1 unit of Mercury per day. You can also find Mercury scattered around the land in small amounts (3-6 units per resource stack).

In Inferno and Conflux towns you can also build the Resource Silo which will bring you 1 Mercury per day.

Rissa is able to produce 1 additional Mercury per day for the Kingdom she serves. Also, any hero equipped with the Everpouring Vial of Mercury gives you 1 Mercury every day.