To complete the Scare-o-Meter you'll need to deploy every scene and have a lot of population idle to scare. Here are 3 tips to complete the scare o meter every day:

1) Assign every monster to the scenes as they will give you more scary faces:

2) Have all the population idle so they can get scared:

3) Have the best Stats possible in the Scare-o-Meter:

The Scare-o-Meter will reward you each milestone with Goosebumps Bills or special Items. You even might find Fear Gems! Fear gems are the most valuable Items in the game.