|“||Taking place in an area called the Mold Threshold, you can see spores and infectious mold taking over the room completely.||”|
–Elise Favis, Game Informer 
The Mold Threshold is a Threshold located in the Oldest House. Within the Threshold are various mold-like growths that pose a threat to the safety of the entire Bureau. The mold is described as the result of incompatible molecular structures from different dimensions interacting, with the dominant one overriding the inferior one. The mold may therefore simply be a form of matter native to an extremely alien dimension. The mold takes over all living things within its range of influence, including humans. In the midst of the Hiss invasion, Jesse Faden entered the Mold Threshold to stop the threat, eventually discovering the source of the mold, a monstrous entity called Mold-1.