L4D2's AI Director, But As A Bowl Of Dice
EDIT: I've learned that the Angry DM has apparently already come up with this idea and has even called it the exact same name. I'm gonna leave this up because it's not like I get any ad revenue off it or anything, and mine is very slightly different, but I'm feeling a bit red in the face, I'll say that much.
TLDR: A game mechanic where every 5 minutes the GM rolls a d6, and if it's not a 1 it gets added to a pot. Once a 1 is rolled, all the dice in the pot get rolled and that's how many zombies / mooks / minions descend on the group.
I have played Grant Howitt's Havoc Brigade many times at this point. It's a blast and I'll run it again for anybody who will sit down at a table with me. It's full of great elegant design choices that support the kind of story it's designed to run. I could talk at length about the way the game handles equipment, how it supports inter-party cooperation, and how it encourages reckless orc hijinks, but it's actually free so you should just check it out for yourself.
The mechanic that impressed me most, though, was the Suspicion Pot. In a nutshell: as the orcs make noise and draw attention, the GM adds dice to the Suspicion Pot. When the orcs get into trouble, the GM can use those dice to roll against their actions, making their lives harder. This represents the increased awareness of the guards in the area and their efforts to heck up their plans. Of course there are ways that the orcs can use this to their advantage, breaking the tension in a big once-per game commitment to chaos, and resetting the status quo. The longer they wait, the more likely they are to succeed in this Hail Mary so in some ways it's to the orcs advantage to play into type and "go loud" as they say.
In a way the Suspicion Pot reminded me a bit of Left For Dead 2's AI Director. In this video game players try to complete levels while hordes of zombies descend upon them from all sides, forcing them to always keep moving, and ensuring they never get complacent. But the zombies aren't constant; they come in waves of varying intensities based on how well the players have been doing. If the players have been on a roll they can trust that soon enough a massive wave of zombies will barrel around a corner. If they've been really struggling they may get a breather, or even some additional weapons and ammo.
I was struck by certain similarities: in L4D2, the longer it's been since you've had to shoot a zombie, the more frightened you become. In Havoc Brigade, the longer you've been causing trouble, the harder things get for you. They are kind of inverse of each other in some ways, but they both promote a mounting tension and a constant impetus to move forward quickly and cautiously.
Here's an adaptation of the Suspicion Pot that mimics the mounting dread of the AI Director. It is a pacing tool rather than a real game mechanic, so I think it could easily be tacked onto most other game systems that don't have explicit pacing rules of their own:
Tension Pool
What you need: A heap of six-sided dice (or whatever, you can tweak this to suit your system), and a big jar or pot.
During some sequence where there's a constant threat of discovery from hordes of enemies (a zombie game, running through an enemy fortress, navigating the bug tunnels, etc), break out the Tension Pool. Every time the players do something scary like open a door or make a loud noise, of if 5 minutes have passed since the last one of those things happened, roll a die:
- If it's NOT a 1, put it in the jar where everyone can see it (it's important for players to be able to see the mounting pile of dice)
- If it IS a 1, stick it in the pot with the rest and then dump the jar out. Count up the pips: that's how many mooks come crawling out of the woodwork. These should be low-level minion monsters that rely on numbers to be threatening, but not so meaninglessly small that the characters can be completely careless about it.
- Optionally, try swapping out any dice that show a 6 with a tougher variant enemy. Maybe rolling boxcars spawns something truly terrifying from which it's best to flee!
If players do something really clever to reduce their risk level such as locking doors behind them or laying traps, you can remove a die from the pool, but generally only allow this if the players are expending something to do so. And if it's something that's going to take a lot of time to accomplish let them know that it's not going to pay off before they try it - lingering around an area is likely going to get them noticed.
Give the players one action each before the bad guys show up: Describe the glowing eyes blinking open in the dark mineshaft, or the sounds of ringing alarm bells and clatter of jackboots and ask them how they spend the remaining 10 seconds before all hell breaks loose.
If your game system doesn't have monsters that are appropriately squishy (where facing 8 of them is considered relatively easy) you can downgrade your dice to d4s, or just count the dice rather than the pips. This reduces some of the randomness as well.
Optionally, you can provide your players with a tantalizing choice: If the dice pool reaches some threshold (let's say 6 dice), let them encounter a room containing treasure... and monsters. If they like, they can try to enter the room, but let them know it'll likely trigger the alarm and cause you to roll the tension pool for enemies. But the treasure inside looks substantial! If they can get inside and deal with the enemies, the dice will be re-rolled before the Tension Pool resets, but instead of spawning monsters use the results to generate loot from the following table (modify to suit your game world):
- Healing item
- Ammunition
- Utility item (spell scroll, zombie pheromone, flashbang, etc.)
- Small treasure item
- Medium treasure item
- Large treasure item
That's it! That's the whole system. For ages I considered writing a whole game around this, but really I don't think it needs it. Like I said before it's a good tack-on system for almost any standard ttrpg. Give it a go and let me know what you think.