From Beyond Zork manual

Moss of Mareilon is a soft, pale fungus which thrives in underground tunnels and public toilets.

It was first classified in 843 GUE by Thwack of Mareilon.

When squeezed, the moss releases an invisible cloud of spores which improve the dexterity of laboratory rats and certain humans; its effects on other species is uncertain.

Moss of Mareilon can be found in the cellar of the Broken Lantern in Grubbo-by-the-Sea, in the underground stomach of the Crocodile Idol, and in caverns in the Mithicus Mountains, and other locations.