Cart-mounted explosive Bomo built for remote delivery into the street, shelved when hunters gained explosion immunity.
Working fast in the Bomber's Studio inside Personal Space, Carl grabbed a cart and pulled it to the door, quickly preparing a wheeled bomb while explaining the plan to Princess Donut. The intent was to roll it into the street outside the saferoom via a clockwork duplicate of Bomo summoned by Clockwork Triplicate, then set it off remotely.
The device never left the room. Vrah's Note on the door revealed all Hunters were now protected from further explosions, so it would only have killed NPCs. Carl apologized — "We'll save your bomb for another time" — and Bomo growled unhappily. This is the same sort of device Carl warned Bomo about at the chapter's opening: stable, but liable to turn into a dud if fiddled with too much before it was time to leave.
An explosive charge mounted on a handcart, ready to be wheeled into position.
The party's intended opening strike against the hunters, cancelled before deployment.