A Defense of Roll Under

I've said it here before, I'm a big fan of GURPS. GURPS stands for "Generic Universal RolePlaying System", and has been part of Steve Jackson Games' product line for more than three decades.

So, it may come a surprise that my first experience with a "roll-under" system came from a relatively unknown game called "Cascade Failure". Where GURPS is a mechanically unique, long-time mainstay of the roleplaying game industry; Cascade Failure is a Sci-Fi d20 game in most respects. In fact, the major deviation from the d20 model is in the fact that the system uses a "roll-under" dice mechanic.

The average player of something like D&D is probably used to the idea of target numbers. You have to roll a 15 or better on, let's say a stealth check, you roll a 20 sided die, add your stealth score, and if you meet or beat a 15, congratulations! You did a sneak!

In a roll-under system, the same logic is applied in a wildly different order. Instead of a DC 15, you might be rolling at a -3. Subtract three from your sneak score, and then try to roll at or below the modified score.

In fairness, this system is a little less intuitive in a couple of ways. Firstly, having to add OR subtract to set the difficulty might feel a little more daunting than just adding your roll to your score. Secondly, for players who are used to hoping for high numbers on a die roll, it can be tricky to flip that switch and think of a 3 (in GURPS) or a 1 (in a d20 system) as a critical success.

Still, I'd argue that in my experience, the benefits have outweighed the negatives. Players who get used to this style will quickly pick up the narrative difficulty of the tasks based on the plus and minus modifiers you call out. It also gives you a good "default" difficulty by having them roll an unmodified check.

More than any of that, and I have no real explanation for this, roll-under combat moves faster. I'm not sure the math behind why it does this, but something just seems to click right when the players are rolling low instead of high. Combat skips along at a wild and cinematic pace, as opposed to the long draw that more traditional systems tend to bog down into.

If you've never tried to re-imagine your gaming in a roll-under model, I'd encourage you to give it a try, and let me know in the comments what you've found to work at your own table.

Happy gaming, all.