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Old 10-18-2020, 08:25 PM   #1
enelsonmo
 
Join Date: Jun 2018
Default GURPS + 4DF

I think it would be fun to use Fudge Dice for action resolution in GURPS. I enjoy tinkering with systems and thought this would be fun to try. Probabilities are all out of whack. Not suitable for those that like their GURPS the way it is.

Action Resolution
1. Roll 4DF and add your skill (Lockpicking 12 for instance). If you total is 10+, you succeed otherwise you fail.
2. Opposed actions have both sides roll and compare their totals. The higher total succeeds at their action. You or your opponent needs at least a 10+ to succeed.

Combat
1. Roll 4DF+Dex for Initiative or you could use Move. My preference is Dex.
2. Roll to hit using your weapon skill.
3. Roll to defend using parry, block or dodge.
4. If the attacker rolls >= opponent, than she hits. And the winning roll must be 10+.

Damage
1. Base weapon damage = Average weapon damage round up.
2. Ex. 2d-2 = 7 (average of 2 dice) - 2 = 5 base damage
3. Roll 4DF and add base damage.
4. Apply this to hit points after subtracting armor.

Special Considerations
1. 4 +'s - Auto success (like rolling a crit if you want)
2. 4 -'s - Auto fail (or a fumble)
3. Combat To Hit - 4 +'s = Double base damage and ignore any - when rolling damage.
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Old 10-18-2020, 08:31 PM   #2
Tyneras
 
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Default Re: GURPS + 4DF

What are fudge dice?
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Old 10-18-2020, 09:20 PM   #3
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Default Re: GURPS + 4DF

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Originally Posted by Tyneras View Post
What are fudge dice?
Six-sided dice with two sides marked '-', two marked '+', and two marked '0'. Rolled 4dF is equivalent to rolling 4d3-8.
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Old 10-18-2020, 11:56 PM   #4
ericbsmith
 
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Default Re: GURPS + 4DF

Quote:
Originally Posted by Rupert View Post
Six-sided dice with two sides marked '-', two marked '+', and two marked '0'. Rolled 4dF is equivalent to rolling 4d3-8.
In that case 4dF doesn't have enough swing to provide a comfortable pass/fail space for skill rolls. Assuming that ++++ always succeeds and ---- always fails, this leave a pass/fail zone of just +3/-3 from whatever target number is set. If the target number is 10 then any effective skill of 13+ always succeeds (except on a ----) while an effective skill of 7- always fails (except on ++++). In order to get a pass/fail zone more in line with GURPS you'd need to roll something like 8 or 10 dice, but then you're drastically flattening the bell curve mechanic of GURPS.
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Old 10-19-2020, 08:37 AM   #5
Anaraxes
 
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Default Re: GURPS + 4DF

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Originally Posted by ericbsmith View Post
Assuming that ++++ always succeeds and ---- always fails
Not usually a FUDGE / FATE assumption as far as I've seen, but if you're trying to be GURPSish you'll certainly need the crits.

If you want to match the percentages, it's even a bit worse. +4 / -4 is a ~1.23% chance on 4dF. Taking +/- 3 or 4 as crits gets you over 6%, a closer match to the 3-5 range (if a little high). But then you'd only have a useful range for the success spectrum or MoS of -2..+2. To really match GURPS, you'd also need a rule that dropped the 3's as crits and just used the fours at low enough skill to parallel the "ten over/under" rule in GURPS.
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Old 10-19-2020, 09:44 AM   #6
Apollonian
 
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Default Re: GURPS + 4DF

How much range do 5Df or 6DF get you?
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Old 10-19-2020, 01:15 PM   #7
ericbsmith
 
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Default Re: GURPS + 4DF

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Originally Posted by Apollonian View Post
How much range do 5Df or 6DF get you?
Every die adds +/-1 to the possible range, but it also makes getting the maximum +/- roll less and less likely. 6DF gives you a range of +/-6, but the chances of rolling 6+ or 6- are 0.13% (1 in 729), which is considerably lower than a GURPS Critical (3&4 or 17&18 are 1 in 54 or about 2%).

So now you need to consider expanding the critical range if you're using Fudge Dice, which reduces the effective range of other possible outcomes. The more dice you add the more the bell curve pushes outcomes to the middle results, too.

Adding two more dice just pushes my earlier example out two more values; so with a Target Number of 10 an automatic success, barring a critical failure, will happen if the skill is 15+, while an automatic failure is at 5-. However, at skill 14 the chances of rolling a -5 and getting a normal failure is just 6 in 729, or about 0.8% (note: not 8%, 0.8%).

To get something close to the GURPS skill ranges as far as expectations of success go you'd need something like 10DF, and on that many dice a roll of +/-6 or greater comes up less than 2% (so you're looking at setting the critical success range at any roll of 6+ and critical failure of any roll of 6-).

Code:
Value	Permutations	% Chance
-10	1		0.00%
-9	10		0.02%
-8	55		0.09%
-7	210		0.36%
-6	615		1.04%
-5	1452		2.46%
-4	2850		4.83%
-3	4740		8.03%
-2	6765		11.46%
-1	8350		14.14%
0	8953		15.16%
1	8350		14.14%
2	6765		11.46%
3	4740		8.03%
4	2850		4.83%
5	1452		2.46%
6	615		1.04%
7	210		0.36%
8	55		0.09%
9	10		0.02%
10	1		0.00%
			
Total	59049
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Old 10-19-2020, 04:48 PM   #8
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Default Re: GURPS + 4DF

One possibility to expand things out would be to use exploding dF’s. Each + you roll gets rerolled, staying a + on a roll of - or 0, but becoming 2 +’s and rerolling again on a +. A - would be treated similarly. Rolling 1dF exploding means a result of 0 33% of the time, a +1 or -1 22% of the time each, a +2 or -2 7.4% of the time each, and so forth. I think rolling something like 3dF exploding might give a curve that isn’t quite so steep, but I’ll leave it to someone else to work out the math on that.
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Old 10-19-2020, 06:44 PM   #9
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Default Re: GURPS + 4DF

Quote:
Originally Posted by ericbsmith View Post
In that case 4dF doesn't have enough swing to provide a comfortable pass/fail space for skill rolls. Assuming that ++++ always succeeds and ---- always fails, this leave a pass/fail zone of just +3/-3 from whatever target number is set. If the target number is 10 then any effective skill of 13+ always succeeds (except on a ----) while an effective skill of 7- always fails (except on ++++). In order to get a pass/fail zone more in line with GURPS you'd need to roll something like 8 or 10 dice, but then you're drastically flattening the bell curve mechanic of GURPS.
They could be 2s instead of 1s. That would make 4 and 16 (due to +6/-6) the 'auto succeed/fail' numbers and that lines up with normal rules.
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Old 10-19-2020, 11:00 PM   #10
ericbsmith
 
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Default Re: GURPS + 4DF

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Originally Posted by kirbwarrior View Post
They could be 2s instead of 1s. That would make 4 and 16 (due to +6/-6) the 'auto succeed/fail' numbers and that lines up with normal rules.
That would create a breakpoint at even numbered skill levels, since odd-numbered skill levels would never matter except in the cases you're taking an odd-numbered skill penalty (or bonus). Assuming that odd- and even-numbered penalties are about equally common.

Honestly, IMO it just changes the core GURPS mechanic too much. If you're looking to do something different I recommend checking out my article on Polyhedral GURPS for inspiration on how to use your D&D shinys with GURPS. These change the core mechanic far less, but allow you to use your fun dice.
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