Sentinel
From Blood on the Clocktower Wiki
Add the Sentinel to your script to keep the number of Outsiders in play mysterious. (For Script games only.)
Character Text
"There might be 1 extra or 1 fewer Outsider in play."
Examples
There are seven players in this game. There are no characters on the character list that add Outsiders. The Demon bluffs as the Saint. A Sentinel is in play, so the good players are not sure if there is actually a Saint or not.
There are nine players in this game. Even though a Baron is on the character list, the good players know no Baron is in play because the Witch just killed a player, so there should be just two Outsiders in play. However, the Outsiders cannot be trusted because a Sentinel is in play. Indeed, there is one less Outsider than normal in this game, and the Witch is bluffing as the Butler.
Explanation
The official character lists are carefully constructed so that the number of Outsiders is never completely known, which lets evil players safely bluff as Outsiders. Many of the games you create using the Script Tool will not have this luxury. If, for one reason or another, the number of Outsiders in a game will become certain, the Storyteller can add a Sentinel. This will confuse matters and help the evil team either bluff as Outsiders or make existing Outsiders look suspicious.
Games with a Sentinel in play might have one more Outsider than normal. They may have one less. They may have the normal amount. It is up to the Storyteller.