In the many secret wars between factions of the Old Ones, the casualties were not always human. Sometimes higher (or lower) beings were destroyed and sent back to the dimensional occultations from which they had emerged. Once such was the mouthing fungus Yub Shugganth.

After it was destroyed by an avatar of Nyarlathotep, its shrinking hide was quickly dunked in fever-brine by the Master of the House and divided up into sections. Some parts went to cover unholy manuscripts and grimoires, others became fashion accessories for decadent ladies of seventeenth century France, and some became the soles of shoes.

A dull green in colour, shoes, boots or other footwear which are soled with the hide of Yub Shugganth allow the wearer to step through shadows into whatever they represent, so if someone was to walk into the shadow of a bank with the intention of travelling through the darkness, they would then appear inside the bank itself, emerging silently from a dark corner.

This only works with the shadows of buildings and other such locations, attempts to walk in the shadows of people have usually ended with the horrific melding of both parties, and if the shadow moves during transition, the traveller is partially fused to whatever surface they were standing on, at the molecular level.