Saturday, May 21, 2016

Arkham Horror Mechanics

Matt Miller 

I've been playing a great deal of Arkham Horror, where a 5 or 6 on a d6 count as a success. Rolling 8 or 9 dice, it takes a bit to pick out successes. But estimating how likely something is to succeed is easy; every dice you roll gives you 1/3 of a success. Which makes it tempting to adapt as a base mechanic for an RPG. But I'd like more than two ways (1) Extra dice, 2) Extra success) to affect a players roll.

Matt Miller 
Arkham has a mechanic which asks you to roll a success. Mentally, it's hard to imagine how that affects the outcome, as it is deeply unintuitive. In effect, it squares your chances. If you roll 1 dice, your chance is 1 in 9 (1/3*1/3). But if you roll 2 dice...I become confused. The probabilities get wonky. Chance of getting 1 success, on X dice, squared, is the match. X*(1/3)^2...I think. If I have 5 dice, the chances of getting 1 success, twice, is not the same as the chance of getting 2 successes on 10 dice; the first is harder.

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