Regular readers know that I love little differences with big effects. Elegance in design is a thing of beauty, and tracing the secondary effects of a small change can yield big results.
Our friend Tesh has a good example with critical hits in Zomblobs! (under development):
Criticals in Zomblobs! happen when all of the dice you roll show the same number. … Most curiously, these criticals are easier to score the fewer dice you roll. Weaker attacks have greater potential to hit a little bigger. This particular “crit” design is therefore more of an “underdog” mechanism, rather than a “win more” mechanism. Instead of harder hits probably hitting even harder, it’s the weak hits that are most likely to slip in a little extra punch.
Simple, elegant, effective. On the other side, it reminds me of the old World of Darkness botch mechanic. Under the previous generation of their system, 1s cancelled out successes, and having negative successes led to a critical failure. Higher skill gave you more dice to roll, and higher difficulty meant needing a higher number to succeed. The net effect was that, for very difficult tasks, having more dice meant a greater botch chance. In some sense, this made sense. If you are an utter novice, it is hard to get far enough in to really mess things up; it is the middling-low range of competence that is really dangerous. On the other hand, you can see the statistical perversity of a system where getting better can hurt you. The designers there did not have the numeracy and/or interest to trace through the effects of their system.