I'm way bored of D&D's pass/fail mechanics. Every dice roll to determine success is a binary yes/no, and while this works fine, it's also missing out on a lot of opportunities for interesting stories. Here is what I mean:
D&D
Player: I want to kick in a door.
DM: Okay roll equal to or less than your STR on a d20.
Player: Okay I succeed. (Or: I failed)
DM: You kick the door in. (Or: You didn't kick the door down)
The very first game I saw that had partial success mechanics was the old, hella excellent sci-fi RPG Alternity. Alternity also used a roll-under a target number on a d20, but it segmented results into marginal success, good success, and amazing success. If you had a Kick Door skill of 12, then your character sheet would list it as 12/6/3, and rolls would work like this:
- 13-20: Failure
- 7-12: Marginal success
- 4-6: Good success
- 1-3: Amazing success
Your result is determined by which type of success you receive, with exact outcomes determined by the GM:
- Marginal success: It takes a couple kicks, and probably makes a lot of noise, but you get the door down. A success by definition, but nothing special.
- Good success: You kick the door down in one blow. Better than marginal success in a quantifiable way.
- Critical success: You kick the door down in one blow, and it doesn't even make any noise. Better than a good success in a quantifiable way.
Now, this is all fine and good, but I think the recently released Dungeon World does a better type of partial success vs full success mechanic. In DW, a partial success gives the player the option to chose from a list of negative modifiers to their success, to show that while it was a success, there was some cost. In DW, there is only partial successes and full successes. One example of this is the Fighter ability Bend Bars/Lift Gates. When a player make a partial success, they chose two options from the following list, while a full success lets them pick three. The list is:
- It doesn't take a very long time
- Nothing of value is damaged
- It doesn't make an inordinate amount of noise
- You can fix the thing again without a lot of effort
While certainly a lot of old school GMs aren't a fan of players choosing these sort of effects, it's still possible to hack a really simple partial success mechanic into D&D.
SICK ASS HOME RULE TIME
Whenever you roll a roll-under attribute check, the goal is to roll as low as possible. The lower the roll, the better chance of landing in a better success category:
- Rolling equal to or less than one quarter of your attribute is a critical success. The action succeeds in such a way that there is an additional benefit to the player.
- Rolling equal to or less than one half of your attribute, but greater than one quarter of your attribute, is a success. The action succeeds as planned.
- Rolling equal to or less than your attribute, but greater than one half of your attribute, is a partial success. The action succeeds, but there is some cost or misfortune associated.
- Rolling greater than your attribute is a failure. The action does not succeed.
The GM should state if you round up or down before the game starts. Rounding down penalizes a player's chance of success by 5%, while rounding up gives a player a 5% bonus. Most grim, brutal fantasy D&D games will round down for added shittiness, while story oriented happy time D&D games will give the player a little break by letting them round up. I'll be assuming rounding up for the remainder of this post.
Oh, and, as per D&D standard, feel free to toss a situation bonus onto the roll. -5 being a substantial bonus (+25% success), +5 being a substantial penalty (-25% success)
Looks, maybe an example would help. Remember our friend trying to kick the door down? Let's say that he is a Fighter with a STR of 16. His success on a STR check are as follows:
- 17+: Failure: The door is still standing.
- 9-16: Partial success: The door is kick open, but perhaps it took a long time and nearby monsters are aware, or perhaps the door fell off it's hinges so it can't be spiked shut.
- 5-8: Success: The door is kicked open. It doesn't take too long, but isn't instantaneous It isn't loud, but it isn't quiet either.
- 1-4: Critical success: The door splinters in one kick, granting surprise on the goblins on the other side.
Partial successes aren't meant to heavily penalize characters, simply add an interesting obstacle or set-back for the players to deal with. A partial success on kicking the door down shouldn't cause a sprained ankle and temporary DEX penalty, but might result in an axe handle being broken while trying to bash the door in. Personally I like to let players suggest their own penalties, although if I think I have a more fun one I will use my own. Here are some examples:
- Hauling a statue out of a hole: Statue damaged in process.
- Leaping over a ledge: Minor item dropped into pick.
- Negotiating with a fence: Item available, but at a mark-up or with additional costs
- Building a trap: Trap is built, but difficult to hide.
- Competing in a contest: Win the contest, but it causes bad blood among rivals.
A critical success should provide an interesting bonus. I'm one of those GMs who thing that bonuses should always be proportionally better than a penalty is, I would make critical successes pretty awesome. The level of "grit" vs heroism you have in your game might vary, and deciding how useful a critical success will be in your game will set the tone somewhat.
- Hauling a statue out of a hole: Proves much easier than expected, takes half the time.
- Leaping over a ledge: Perfect landing and hits the ground running. Can act again this round.
- Negotiating with a fence: Item available and available cheaply or with no strings attached
- Building a trap: Trap is built, easy to hide, and proves more deadly than expected
- Competing in a contest: Win the contest in a way that amazes the spectators. Congratulations all around.
Oh, and since it will invariably come up: If you can't think of a partial or critical success result, it's really fine to just make it into a normal success. Or ask the players, they might have an interesting idea.
LETS TALK ABOUT THE MATH
It's obvious that roll-under attribute checks benefit characters with a higher attribute. You can easily determine your chance of success by multiplying your attribute by 5 to get your percentage chance to succeed. A character with lowly 3 has only a 15% chance, while an "average" attribute of 10 is a 50% chance, and a mighty 18 is a full 90% chance of success.
Now, a tiered success system has an additional benefit to characters with a high attribute. A character with an attribute of 18 critically succeeds 25% of the time, while an average attribute 10 has only a 15% chance of a critical success, and a character with an attribute of 4 or less only critically succeeds 5% of the time.
The other interesting thing about the math is that a character's success is a partial success half the time. This means that even a character with an 18 partially succeeds 45% of the time the attempt a check. I think this actually works okay, simply because I think minor set-backs or complications actually make the story more interesting, and besides, every time that 18 attribute character succeeds they are getting a full or better success half the time, or 45% chance on any given attribute check.
HOW TO HACK YOUR OWN SICK AS HOMERULE
Hey, maybe you hate doing math. How about equal to half or less is a critical success, while over than and up to equal to the attribute is a normal success? Our door kicking fighter's 16 STR is now
- 17+: Failure
- 9-16: Success
- 1-8: Critical success
Maybe you like letting players effect the narrative, as opposed to D&D's classic simulationist gameplay. How about taking a note from Dungeon World and instead of declaring the effect of a partial or critical success, you list a couple of options and let the players choose?
Hey, maybe you like playing miserable "dungeon fucking Vietnam" games and what everyone do be horrible (Level 0 DCC games!). How about removing critical successes but keeping partial successes?
- 17+: Failure
- 9-16: Partial success
- 1-8: Normal success
Want to make an even more miserable dungeon Vietnam game? Add a critical failure level by halving the failure tier. This makes characters with low attributes suffer disaster more often, while characters with a high attribute have only a small chance of a critical failure.
- 19-20: Critical failure
- 17-18: Failure
- 9-16: Partial success
- 1-8: Normal success