Art from https://www.artstation.com/artwork/04omB4 by Teodora Anghel

Let's jump straight into it with parts five and six: How did it happen, and most importantly what clues are available for the party?

(and of course a BBEG).

How Did the Crime Happen?

Somewhere in between the show starting and the meet and greet at the start of the session. Vivienne was kidnapped so that they would violate safety standards, and the fines would force Uncle Matt to sell the castle, which Garrett will gladly buy. There is a secret gold mine that he wants, that he has used to keep Vivienne, and she is being guarded by his programmed dragon construct.

What Clues are Available?

Here's a breakdown of the clues, and like secrets from Lazy GM, I like to have a general idea of where these secrets might be, but keep it flexible so that players don't get stuck at any one location:

1. Torvin has spent more money than needed for the production purchasing more parts. This can be found out by discovering receipts for the production. If the party finds receipts or asks Torvin, he is initially hesitant to tell the party, but may reveal that he was asked to by Garrett
2. An old map hidden away that shows secret passageways below the castle. Implies a deep cavern complex below, but not what's inside.
3. Any of the Dogs may smell gold dust on Garrett's clothes.
4. All the producers and Uncle Matt were shown the machinery of the stage multiple times. They are likely at least capable of having learnt how the machines work.
5. Rufus would have a tiny dragon model. This was made as a backup, in case the illusory stones wouldn't work for the one-woman show. While he never needed to build a larger dragon, it is noted that the schematics are missing. It is with Garrett.
6. Mx. Whisper would know that the only people capable of rigging the show are the producers, Rufus, and maybe Torvin.
   
7. Brother Aldric will have tales of a great dragon guarding treasures implying the existence of gold below the castle. This is also what motivated Garrett to investigate the mountains for treasure.
8. Shining candlelight at an angle at Vivienne's room mirror will reveal text saying "THE DRAGON KNOWS YOUR SECRETS". She had been scared here, and taken through a secret passage way to the caves.
9. Speaking to Marta would reveal that Garrett refused to sign on the insurance contract - forcing Matthew and Leonard to be fully liable if something wrong were to happen.
10. Garrett will go missing every now and then. No need to imply this during the game, but players can make history checks in the late game to realize that he was left unaccounted for several times. He would have been checking on his gold, and slipping through exits.

If after all this, your players STILL can't find out who the villain is, when you have about 30 minutes to an hour left of game time, I'd have a scream be heard, and the party directed to a secret passage that leads to the gold cave, and just start the...

BBEG Fight.

It's gonna be a dragon. Duh. A clockwork dragon. Up until now, there were most probably basically no fights, so we gotta have one big fat flashy fight here. CR5-ish would be a threat for Level 3 Characters, possibly knock them out, but it shouldn't be too much of a fight that it outright kills anyone (don't play this creature too intelligently either, it's just a prototype magic robot that was designed for entertainment, not battle. If anything, just pick the flashiest attacks, and go from there.

So here's a little quick primer on how I create monsters from scratch. Firstly, figure out how hard you want the fight to be. We've already picked a difficult fight for level 3 characters. This starts with hit points and constitution - on average, a group of a level 3 Fighter, Cleric, Wizard, and Rogue at level 3 will do about 40-ish damage (let me know if you're interested in this kind of D&D math, and maybe I'll mention it in a future blog post) per round. A CR5 creature is typically equivalent to a roughly level 10 to 11 character. So we'll give it 11 hit dice, and for a large creature it's a d10 hit die, which should average out around 100 hit points, after constitution of +3 to +5. This means that on average, the party will take about 3 to 4 rounds to defeat it, assuming average rolls. This would be 1 or 2 rounds with good critical hits, or 5 to 7 rounds if the party sucks at rolling dice and have skill issues there. Generally, this is a good rule of thumb for 4 party members, and makes it an okay fight for, let's say a full party of 6. I'd bump the hit points towards the 140 side for a 6 man party, and towards the 60 to 80 mark for 3 or less players.

Then, we gotta decide how we want it to hit. As a dragon, we want a breath weapon, so let's start there. The average character's hit points is going to be between 19-ish (for the wizard) to 29-ish (for the fighter) and in between for any other classes (except for Barbarians that go over 30. We want this breath weapon to go somewhere in between on average, leaning closer to the wizards hit points (cause sometimes... DMs roll really well). 4d10 or 4d8 seems to be the sweet spot here, average at 22 damage. Of course, if you the DM rolls really well, it's gonna do 40 damage, and even on a successful save, it's 20 damage. Devastating for any group, but hopefully the cleric is fine, and can get everyone back. The DC for this will be 8 + proficiency (+3) + the creatures Constitution (since the breath weapon comes from the "body" of the creature. We want the DC to be about 15 (at this level most characters have a -1 to +3 for Dexterity saving throws, so 40% of the time-ish, the party succeeds). This means that our Constitution has to be +3, or 16/17. We can calculate the hit points from here to be on average 93 (with 11d10 +33). One ability score down, and HP is good!

After the breath weapon, which needs to recharge, we can give it a claw and tail attack - similar to a T-Rex, so that we aren't plowing down on any single character. Let's give it a Strength of +4 so that it rolls a +7 to hit. This should hit most Level 3 characters pretty consistently. 1d12 or 2d6 plus 4 damage averages around 10 to 11 damage per round. This means it will likely take down one person after their breath weapon, per hit. Hopefully your players are smart enough to not a) crowd together and b) know to keep distance if they can. 

Let's keep the Dexterity average at +0 so that it's more likely to get a middling number for initiative.  We have all the "physical" stats down, let's speed run the "mental" stats, since we don't have to worry about spell casting for this creature.

Let's go with slightly above Int and Wis since this is a robot dragon that can understand performances and audiences. A 12 or 13 is good enough here. Let's bump the charisma up a bit more, since it's a performer, and should have at least a slightly above average Performance skill (which we'll also give proficiency for. A regular movement speed and double fly speed would be scary too!

Lastly, let's give it an ability relating to the illusion stones that are imbued into it. A straightforward insight against deception - this creature isn't great at lying, but just like CGI, viewers know half the time if it's real or not.

For this specific dragon, we do have illusions of Vivienne, and may some of the other people that the party has met, and perhaps could use this to distract players, but if the players already know who the bad guy is (or the session is ending), we have more than enough fight in this guy.

Here's the dragon~

"Dragon" of the Forbidden Mountain

Large Construct, True Neutral

Armour Class - 15 (natural armor)

Hit Points - 93 (11d10 + 33)

Speed - 30 ft.  fly 60 ft.

STR   18 (+4)

DEX   10 (+0)

CON 16 (+3)

INT    13 (+1)

WIS   12 (+1)

CHA  14 (+2)

Saves DEX +3, CON +6, WIS +4, CHA +5

Skills Deception +5, Stealth +3, Performance +5

Senses blindsight 30 ft., darkvision 60 ft., passive Perception 11

Languages Understands the languages of its creator but can't speak

Challenge 5 (1,800 XP)

Proficiency Bonus +3

Traits

Illusory Mimicry.

The dragon can mimic sounds it has recorded, including voices and it can recreate images as illusions that it has recorded. A creature  can tell the sound is an imitation with a successful Wisdom (Insight) check opposed by the dragon’s Charisma (Deception) check.

Actions

Multiattack. 

The dragon makes two attacks, one with its bite and one with its claws.

Claw.

Melee Weapon Attack: +7 to hit, reach 5 ft., one creature.

Hit: 11 (2d6 + 4) slashing damage.

Tail.

Melee Weapon Attack: +7 to hit, reach 5 ft., one creature.

Hit: 10 (1d12 + 4) piercing damage and the target must succeed on a DC 15 Dexterity saving throw or be knocked prone.

Fireworks Breath (Recharge 5–6).

Wisdom Saving Throw: DC 14, each creature in a 15-foot Cone. Failure: 22 (4d10) Fire damage, and the target has the Frightened condition until the end of the dragon's next turn. Success: Half damage only.

FIN.

Ultimately, you'll need a little spiel too at the end. Sorry to those who've played in my game and missed this, it took me awhile to figure out what to say...

"You meddling kids! Yes, I created the dragon! But I'm not just some common criminal - I'm a businessman! When I invested in this ridiculous play, I discovered the mine shaft legend. Do you know what's down there? A vein of gold ore worth THOUSANDS! Leonard was too stupid to realize what he was sitting on!

And I would have gotten away with it too, if it weren't for you meddling adventurers and that/those mangy dog(s)!"

That's all folks - will link the document when it's done here. It's gonna take a bit to organise the information properly. Don't forget, who's awesome? You're awesome.