The Haunted Bell is a block that highlights mob spawnable spots when held or rang.
When the Bell is rung (right-click), it will create soul fire particles in spaces where hostile mobs can spawn in a large radius around itself. It can also be held in the main or offhand to continuously highlight spawnable spaces around the player, albeit in a smaller radius.
Haunted bells can also be used on Contraptions to highlight mob spawn-able points every time they toll.
Release 0.3.2: Added.