Append to the rule locations:

As an action a Trick-or-Treater may spend 1 Trick or 1 Treat to Sneak, or change their location once. A Trick-or-Treater may only change to a location that their current location has a connection to. By sneaking, they do not trigger any special rules, except for those that specifically mention sneaking. Their location must be prefixed with an asterisk (*) in the GDNT to indicate they’ve sneaked there, and are hidden.

If a Trick-or-Treater is hiding in a Location (an asterisk (*) prefixes their location) they may not walk. Instead they must either (a) sneak out, (b) pay one Treat to reveal themselves, and do which ever action would be normally won entering that location, or (c) pay one Trick to scare that location.