Nightmare Bell
A bell found within the Shelter — ring it at your own risk.
Ringing it
Like a normal bell, it rings if you right-click it or hit it with a projectile. Doing so inflicts the Nightmare effect on you for 30 seconds.
Nightmare effect
While it's active, aggressive Phantoms spawn above and around you every 5 seconds, immediately targeting you. There's no known way to remove it early — just survive until it wears off.