Boo-Urn

The is a Tool in. Using one while inside a building spawns 1 to 4 Ghosts within it (depending on the building's size), which will start Neutral to the player as ghosts usually are.

Immediately afterward, every NPC inside the building will run out of that building and will then wander around the rest of the floor, never returning to the now-haunted building. The Ghosts themselves will remain inside the building they were summoned into.

Quotes
"I need to be indoors for this to work."

- When attempting to use the Boo-Urn outside of any buildings

"I think this place is haunted enough."

- When trying to use the Boo-Urn twice in the same building.