Night of the Thirteenth

What is Night of the Thirteenth?

Night of the Thirteenth is a slasher-horror TTRPG by Petri Leinonen using a unique d13 system (d10+d4) and a standard card deck to simulate a horror movie cast's likely doom.

You are there to play a character in a movie that hasn't happened yet. It assumes you know something about TTRPGs and does not walk you through everything.

How do you set up the game?

Setting up the game is a quick process of preparing the atmosphere and the tools of your demise. Start by selecting a Playset, which determines the horror sub-genre and setting you will be inhabiting (e.g., Cabin in the Woods or Prom Night).

The Director then constructs the Threat Deck by shuffling all 2s, 3s, 4s, and one Jack together, placing the four Aces face up on top to signal the start. The Reserves (5s-10s, remaining Face Cards, and Jokers) are set aside for later escalation. Finally, establish the Trophy Pile by placing a random 10 face up; this sets the initial difficulty for the Killer. Once the players create their characters by choosing a name, Archetype, and Aptitude, the night begins.

How does the d13 system work?

The game uses a specialized dice system designed to produce both a numerical result and a narrative consequence in a single roll.

• The Formula: d13 = d10 (0-9) + d4 (1-4)
• The Dice: d10 is the main die, d4 is the Fallout Die
• The Constraint: Modifiers cannot push a die outside its natural range.
• Fallout Logic: High rolls are worse. A 4 on the Fallout Die (d4) is "Dire" and is the primary source of Strikes.

What is the Threat Deck?

The Threat Deck is the engine of the game's horror. The top card is always visible, serving as the current Threat Card that dictates the next challenge the players will face.

The suit of the card determines the nature of the challenge and corresponds to the varied strengths of horror movie archetypes.

The value of the card dictates Severity. 1–4 are merely atmospheric, while 5–7 represent dangerous tasks. 8–10 are difficult challenges. If a Face Card appears, you are no longer dealing with the environment; you are confronting the Killer.

How do you resolve a Test?

When you attempt something risky, you make a Test by rolling your d13. If your total is equal to or greater than the difficulty on the Threat Card, you Succeed. If it is less, you Fail.

However, the Fallout Die (the d4 from your roll) determines the quality of that result. A low fallout represents a clean, professional job, while a high fallout indicates a messy, noisy, or even disastrous outcome.

How do you survive (or die)?

This is an Ashcan TTRPG, meaning it's a raw, playable prototype aimed at capturing a specific feel—specifically, the high lethality of 80s slashers. Death is tracked through a simple "Three Strikes" system.

What happens in the Endgame?

If you manage to defeat the Killer in all four suits (Spades, Hearts, Clubs, Diamonds), the Endgame is triggered. All number cards are removed from the deck, leaving only the Face Cards, and the Red Joker and Black Joker are shuffled in.

The game shifts to a final series of desperate rolls. Drawing the Black Joker represents a final twist—a last attempt to turn the tables where success removes a Face Card. Drawing the Red Joker is the true finale: success means you survive to see the dawn, while failure means your character dies just moments before the credits roll.

Quick Facts

• Who is the Director? The person playing the killer, describing the world, and managing the card decks.
• What is a Strike? A mechanic representing a close call with death; three strikes result in character death.
• What are Genre Points? Tokens the Director awards for playing into tropes. Spend one to reroll with +1.
• What is the Trophy Pile? A face-up pile where defeated cards go. Its top card sets the base difficulty for the Killer.