19 February 2017

5d20 Action Resolution for RPGs

Here's a little action resolution mechanic I've been thinking about as the skeleton for a homebrew RPG.  I'm posting it here because I'm not entirely happy with the combat/damage and thought perhaps a reader could suggest a fix.

OK, to set boundaries, let me say that I've embraced the "rules-light" movement and want my system to focus on storytelling not number crunching.  Also, this system fits settings dominated by "normal humans"; it probably would fall apart trying to replicate super-powered settings (Nothing I come up with beats the SAGA system for Marvel).

I won't go into character creation; suffice it to say characters in the system have Action scores ranging from 1 to 19 with higher being better.  A future post will detail some curious die score distributions I found with 5d20 that work well for attribute generation.

The GM assigns one of seven difficulty levels to the task.  The levels are:


Seven difficulty levels exist for completeness and symmetry but as stated above, this homebrew RPG would attempt to maximize description and minimize dice rolls.  So anything Automatic or Trivial generally happens without a die roll; conversely anything Heroic or Impossible generally can't happen without spending some type of finite "hero point" resource or such.  So the middle three difficulty levels are really the only ones that typically require a dice roll.

Once the difficulty level is established, 5d20 are rolled.  Two dice are discarded and the remaining three dice are considered individually against the character's Action score.  Each die score exceeding the Action score is a failure, equal and under counts as a success.  The total number of successes can therefore be 0 to 3.

Exactly which two dice are discarded depends on the difficulty level of the task.  A Mundane task results in discard of the two highest dice.  A player rolling against a Difficult task discards the highest and lowest dice, leaving the middle three.  Finally, a Daunting task results in discard of the lowest two dice.

The four possible success totals (0 to 3) correspond to the four levels of success (or failure):

3 successful dice: Total Success
2 successful dice: Modest Success
1 successful dice: Near Failure
0 successful dice: Total Failure

The specific definition of each of the above levels depends on the task really and is up to the GM to describe.  The important point is the resolution system isn't binary and allows for gradients of success.  Success gradients are featured in many games but the three-tiered structure presented here was most directly influenced by the first edition Prime Directive RPG.

What about the four other difficulty levels, the two higher than Daunting and lower than Mundane?  Well, as stated before they should be exceedingly rare: either ignored on the low end and out of reach on the high end.  If a roll absolutely needs to be made, 5d20 are rolled as before with Automatic and Trivial tasks using the same dice-discard scheme as Mundane tasks, while Heroic and Impossible tasks use the same scheme as Daunting tasks.  The difference comes in how the success totals are interpreted.  For each difficulty level above Daunting, one successful die roll is ignored.  So the best a character could hope for at a Heroic task is a Modest Success, and could get no better than a Near Failure at an Impossible task.  This is where a hero-point mechanic would come in, with a successful die roll being "purchased" to increase the Success Level.  On the flip side, for each difficulty level below Mundane, one successful die roll is added to the total.  Therefore Trivial tasks can suffer no worse than Near Failure, Automatic tasks no worse than Modest Success.

I've messed around with non-combat situations and the system outlined above seems to work fine.  Opposed rolls are easy: simply assume the middle difficulty level (Difficult) for each character and roll normally with the higher number of successes winning.

I'm not entirely sold on how it works with combat however because no damage mechanic has been developed.  I've been reading the old Ghostbusters RPG (West End Games) and I like the idea of damage being taken against the same finite resource noted above (hero points or whatever you want to call them).  I'm also a big fan of directly reducing Attribute scores, or at least the idea of it.  Unfortunately that path seems to involve a lot more record-keeping.

If you've made it this far and can think of a good damage mechanic, let me know.