The Runners - Mimic chests (Patreon)

Long fang explains. "Our mistress in hear early days bread a specific kind of mimic, one which was less aggressive and more akin to a loyal pack animal. Far faster and more intelligent than most, we call them 'The Runners'"

Blowing a silver whistle in a specific pattern, you slowly hear the sound of approaching footsteps... a lot of them. Suddenly, from a side entrance, something leaps into the room. Similar to a normal chest in every way aside from the large number of feet beneath it. It skids to a halt next to long fang, grinning up at him expectantly 

Long fang reaches out, petting it affectionately, it opens to reveal its contents. "These make theft from our vaults far more difficult."