So, I recently read about the Shadow Creature template from Bestiary 4 and I love the idea of it. So much so I'm doing a "holiday themed" one shot story for my party in January.
The Premise: During the end of the year festival of a small bordertown, a random lottery is drawn from the townspeople to have a banquet with the baroness. The party members, and two guests each, have won this lottery and are asked to come to the baroness' manor for a feast, gifts, and an afternoon of pleasurable activities.
The Plot: During these activities a bard and fortuneteller of sorts draws the entire banquet table into the Plane of Night. If the party succeeds, twas nothing more than a dream. If the party fails, they too become shadows of the plane.
To escape there will be three encounters: The Past, The Present and The Future.
The Past: the enemies will attempt to taunt the party about their past failings and issues.
The Present: the enemies will point out the issues in the party members' current lives.
The Future: the enemies will give grave warnings.
Now for the crux of the situation: I know what the planar rules will be already. I can make some good tactical and different environments. Creative ways to defeat the environment is the order of the day. However, I am not so good with monsters or CR or anything like that.
I would like some advice on what monsters to use with the shadow templates for the Past, Present, and Future events that would challenge a group of very experienced players at level 3. Character creation was based on the Harrowing Method in Wayfinder #5. Kind of like randomly rolling. The group has 3 players in it.