Knowing the Odds

Guest Article written by Zach Remen

As many investigators have realized, Arkham Horror: The Card Game is more than just a deck building game. To rid Arkham of the dark forces that otherwise lurk beyond our comprehension, investigators must carefully choose how they spend their turns as time is not on their side. Underlying much of what they do, however, is the chaos bag. With each and every skill test made, the chaos bag imposes its harsh interpretation of chance upon any investigator who delves too deep.

Mercifully, unlike most things within the mythos, chance is one thing investigators can understand. The Arkham Horror LCG Skill Test & Chaos Calculator is designed to equip investigators with that knowledge to triumph over the odds. The calculator will show you exactly what your odds are of passing (and failing) a skill check based on your current stats, assets, and committed skills. While some investigators may prefer to “Han Solo” their way through the game (“never tell me the odds!”) doing so would be a mistake. Investigators need not consult a calculator with every test, however understanding how probabilities work in the game can inform your in-game choices and deck building decisions.

There are two components that make up a test’s difficulty: (1) the difficulty value, and (2) the chaos bag. The difficulty value serves only as a baseline for the chaos bag which in turn provides the probability of success/failure. The only difference between a difficulty of 2 and 4 is the latter has a higher baseline for investigators to meet. The true nemesis is the chaos bag.

This leads to the most important concept for investigators to learn about: breakpoints. All stat boosts are equal, but their impact on the chaos bag is often not; +1 may give you a 20% boost to your success rate, whereas +2 may only provide a 25%  boost (a net gain of only 5%!). This is because the chaos bag is not equal. There are many tokens in the bag, some of which share the same modifier. Because there are more of these tokens than others, there is a higher chance you will draw this modifier tokens than others. Therefore, having sufficient skill to succeed if one of these tokens is drawn will give you greater boosts to your success rate. For example, on standard difficulty there are two -2’s but only one -3; therefore, going from +1 to +2 will give you twice the boost that +2 to +3 would.

Breakpoints: skill +/- committed to the test above/below the difficulty
  -1 0 1 2 3 4 5 6 7
Success 6.25% 37.50% 62.50% 81.25% 87.50% 93.75% 93.75% 93.75% 93.75%
Success >= 2 6.25% 37.50% 62.50% 81.25% 87.50% 93.75% 93.75%
Success >= 3 6.25% 37.50% 62.50% 81.25% 87.50% 93.75%

Setup: The Gathering (Night of the Zealots) on Standard, Elder Sign = 0

Understanding where these breakpoints lie is important for investigators to know in evaluating just how much they wish to commit to a test. If you know your success change is >70% then maybe you want to hold back that skill card for another test. You can also look at Talent Boosting cards like Physical Training and Hyperawareness and decide just how impactful spending resources on a boost will actually be. You can also use this information when building your deck; maybe those talent cards and neutral skill cards don’t seem so necessary after all, or maybe they are the only way you will hit these breakpoints.

We can also more accurately scrutinize some of the player cards available. Some cards have a conditional effect if the investigator succeeds (or fails) at a test by a certain amount. These are cards like Switchblade, .41 Derringer, Lucky!, and Scavenging. Probabilities inform just how often we will realize that conditional effect, and how valuable that card truly is. A good (negative) example is Opportunist. Opportunist is a rogue skill card with a wild skill icon which states that if the player succeeds at a skill test by 3 or more, they may return Opportunist back to their hand. At first glimpse, the card appears to grant investigators a chance of a reusable +1 bonus. The problem is the math, as seen above.

By the time Opportunist has even a chance of returning to your hand, the investigator already has pretty good odds of passing the test. This is because these conditional effects use the same breakpoints, except their condition is added to the difficulty value. For example, if you’re trying to pass a 2 difficulty value test and want to use Opportunist, you have to think of the test difficulty as 5 (2 difficulty value + 3 Opportunist condition). Consequently, to have any realistic chance of triggering the card effect, you need to commit at least 5 if not more to “succeed” at getting Opportunist back.

These aren’t all bad, however. The reception to new comer Rex Murphy and his investigator specific ability has been a bit mixed. However, his base intellect of 4 gives him a fair chance of triggering the ability on 2 shroud locations. Furthermore, unlike Opportunist and its player card ilk, Rex’s ability didn’t cost you any resources, actions, or cards to use. However, it should be noted that these sorts of cards scale poorly on higher difficulties. In our example, Rex currently has a 37.5% chance to trigger his response ability. On Expert, this becomes only 16.67% (50% chance to succeed the test).

Probabilities also serve as a reminder at just how ineffective the investigator’s Elder Sign may be. This is especially the case with modifier-based abilities like Roland, Agnes, and Jenny. This is because the Elder Sign is (usually) at least a 0 which is usually enough for an investigator to succeed. Unless you’re hopelessly outmatched by the test’s difficulty value or you need to overkill on committed skill (see above), the Elder Sign modifier probably won’t do all that much for you.

Shotgun Damage Range      
0 Damage (Fail) 12.50% Kill Chance Friendly Fire
1 Damage (Min) 25.00% 1 health 25.00% 6.25%
2 Damage 25.00% 2 health 62.50% 0.00%
3 Damage 31.25% 3 health 37.50% 0.00%
4 Damage 6.25% 4 health 6.25% 6.25%
5 Damage (Max) 0.00% 5 health 0.00% 0.00%

Roland using a Shotgun (+7 combat) on a 4 test enemy (same setup as above)

The exception, of course, is the Shotgun where the math gets increasingly complicated. Considering investigators hopes for massive damage (and the chance for some disastrous friendly fire), the Shotgun is the best example for why understanding the probabilities behind the chaos bag is important and why (sometimes) a calculator should be referred to. The Shotgun can be an amazing weapon, but to do that it needs help, and probabilities inform how much help it needs. The Skill Test & Chaos Calculator makes this easy.

One last final thought on probabilities, for those investigators who haven’t considered. Some cards like Baseball Bat, Shriveling, and Final Rhapsody have conditional effects when particular tokens are drawn. As tokens are added to the bag either via scenario instructions or the difficulty chosen, the odds of these happening will change. For example, the odds of taking horror when using Shriveling actually goes down on Expert due to the additional tokens in the bag. More amusingly, Final Rhapsody is a greater danger to Jim Culver on Easy (3/16) than Expert (3/18) (*Note: this is a reflection of the tokens involved, not the math). The sword cuts both ways, however; a card like Ritual Candles that affects only particular tokens may become less effective as additional modifier tokens are added to the bag.

There are a slew of other chaos bag questions that probabilities provide answers to. How good is Wendy’s ability? Are Ritual Candles really worth it? What are the odds the Baseball Bat will break? Will Jim survive the Final Rhapsody? All these questions (and maybe 3 more) can be answered by the Arkham Horror LCG Skill Test & Chaos Calculator.

Get the Chaos Calculator HERE!

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