Pathfinder 1E 3d6 instead of 1d20

Morrus · Jan 10, 2016

N'raac said:
Further reflection: kiss Critical Hits goodbye unless you revamp those rules. a Nat 20 comes up 5% of the time on a d20. 19/18? 10%/15%.

An 18 on 3d6 is one in 216 (under 0.5%) and a 17 is 4 chances in 216 (so about 1.85%).

What are the chances of rolling two or more sixes on 3d6? Maybe crits could be linked to double-sixes instead.

Ruzak · Jan 10, 2016

Morrus said:
What are the chances of rolling two or more sixes on 3d6? Maybe crits could be linked to double-sixes instead.

7.4% = 16/216
Pretty reasonable. You could also require a hit for it to be a critical, which would lower it a bit.

Desh-Rae-Halra · Jan 10, 2016

If you really want the bell curve in d20, how about having people roll 6d4-4? You still dont get a 1 for "fumble", but you just make it a 2.
Yes, getting a nat 20 would be rare, but in a bell curve, that's 2 or 3 standard deviations, so it should be.
If you are changing this on your players, you should tell them to almost never critical hit, and when it happens, it should be a pretty significant event ( more than double damage): like something from Prowlers and Paragons The player gets to narrate what happens

Desh-Rae-Halra · Jan 10, 2016

Morrus said:
What are the chances of rolling two or more sixes on 3d6? Maybe crits could be linked to double-sixes instead.

Neat idea: in thinking about this and my 6d4-4 suggestion, you could also add a poker style element where bonuses come from poker type results: three-of-a-kind, full house, four-of-a-kind, two pairs....

Koloth · Jan 10, 2016

Rather then trying to fit 3d6 to a game system with many years of debugging based on 1d20 for the primary randomizer, play a game designed from the ground up for 3d6. GURPS is one. You can download a free copy of GURPS Lite from Steve Jackson Games. There are so many little things baked into the d20 rule system that will break or bend in funny ways if 3d6 are used. GURPS Lite will give you a good idea on how to handle things like critical success and failure and how to have the stat scores work better with 3d6. You can also search for 'Convert d20 to GURPS' articles to find other issues that will pop up.

N'raac · Jan 10, 2016

I'm assuming "highest roll" as a potential critical and lowest as "always fails to hit or save", but you're right that you can't roll 1 or 20 at all. A lot of the rules would need to be revised.

GURPS excuse me or Hero System strike me as likely candidates. But translating D&D to these systems is likely to carry similar challenges.

N'raac · Jan 10, 2016

Ruzak said:
7.4% = 16/216
Pretty reasonable. You could also require a hit for it to be a critical, which would lower it a bit.

Rolling a 13 (6-6-1) as a potential critical hit when a 16 (6-5-5) is not may offend the senses of anyone who wants "high roll = better roll) to be maintained, but it's a possible approach. Dealing with weapons that Crit on an 18 or 19+, and dealing with Improved Critical, will also need to be addressed.

Any and all of these issues CAN be addressed, but if the goal in doing so is to re-create similar probabilities, it will be a lot of work. What's the objective of making the change? Maybe some of these rules have to suffer marked probability changes, or even be removed entirely, to reach that goal. If the goal is "more predictable, less swingy results", that probably suggests removal of crit's rather than some new means of retaining them.

Illithidbix · Jan 11, 2016

It does lead to an odd thing that the "value" of +1 ceases to be +5% and varies depending upon what number you want need to roll. I believe it gives the "most percentile" benefit when you need to roll a 10+ or 11+ on the 3d6.

Also could lead to very tiresome fights between high AC monsters and players trying to hit each other.
If you're rolling D20+4 to hit AC: 20 you hit on 16-20; so 20% chance or an average of one hit in five attacks.
If you're rolling 3d6+4 to hit AC: 20 you hit on 16-18: so 4.62% change, so on average less than one hit in twenty attacks.

Threat Range Maths! Wheee!
The other thing is critical threat ranges (and similar) need adjusting to accommodate the new probabilities.

Rolling a D20 has 20 different possibilities, rolling 3d6 leads to 216 different ways the dice can fall.
This is useful for corresponding probabilities.
http://www.thedarkfortress.co.uk/tech_reports/3_dice_rolls.htm#.VpMFpxWLS70

I believe
3d6
18= 0.46%
17-18 = 1.85%
16-18 = 4.62%
15-18 = 9.25%
14-18 = 16.20%
13-18 = 25.92%
12-18 = 37.50%
11-18 = 50%

Compared to the rather simpler:
20 = 5%
19-20 = 10%
18-20 = 15%
17-20 = 20%
16-20 = 25%
15-20 = 30%

Which actually is a lot better mapping than I first guessed
(although 17-20 is awkward)

So equivalence:

"Natural 20" = "Natural 16-18"
"Natural 19-20" = "Natural 15-18" (Long Swords/Short Swords etc)
"Natural 18-20" = "Natural 14-18" (Rapiers)
"Natural 17-20" = Uh "Natural 14-18 and flip a coin with a natural 13?"
"Natural 16-20" = "Natural 13-18"
"Natural 15-20" = Again somewhat awkward "Natural 13-18 and flip a coin with a natural 12?"

Similarly a "Natural 1" on a D20 has similar probabilities to "Natural 3-5"

Apparently Improved Critical/Keen Weapons helpfully get Critical threats into the awkward numbers "A threat range of 20 becomes 19-20, a threat range of 19-20 becomes 17-20, and a threat range of 18-20 becomes 15-20."

PurpleDragonKnight · Jan 11, 2016

Illithidbix said:
Also could lead to very tiresome fights between high AC monsters and players trying to hit each other.
If you're rolling D20+4 to hit AC: 20 you hit on 16-20; so 20% chance or an average of one hit in five attacks.
If you're rolling 3d6+4 to hit AC: 20 you hit on 16-18: so 4.62% change, so on average less than one hit in twenty attacks.

Spot on: and this is the main reason that the 3d6 method sucks bananas big time.