Steve Jackson Games Forums - View Single Post

GodlessRose · 03-29-2009, 04:59 AM

I'm kind of enthused at the prospect of running CoC with GURPS, even though we haven't played yet. (Had to reschedule the game for next Friday.) I've been looking over the rules and I've typed up some notes. Nothing revolutionary here, but I figure I'll post them for anyone who's interested. I'll be using the rules in Cthulhu Lives!, with the following modifications. Some of these ideas were appropriated from other contributors to this thread, most notably Gollum. (Thanks!)

Character Creation:
Starting characters are 100 points. Advantages are limited according to Keeping It Real by Paul Blackwell on pg. 31 of issue 3/21 of Pyramid magazine. [This is to make suspense a little easier to maintain, while still allowing players a wide range of character creation options. But if you don't have that issue, don't worry about it. The impact is small, and some would prefer the pulp feel of the standard rules anyway.]

The Mythos Awareness Advantage from GURPS CthulhuPunk does not exist. [I don't think it fits the genre.] The Innsmouth Look Disadvantage is tricky to write up and I doubt anyone would want it, so I'll ignore it for now.

Fright Checks:
When making a Fright Check, refer to the sanity loss for a failed roll in the BRP system. The character receives a penalty equal to (maximum possible die roll)/2, provided the max roll is no more than 24. For higher rolls, the penalty is 10 + (Maximum possible die roll)/10. If a roll has a modifier (e.g., 1d6+1) then double the modifier for this purpose (so 1d6+1 becomes 1d6+2). If the Fright Check is due to a corpse or other mundane cause, however, use the standard GURPS modifiers instead.

The rules for Stress, Derangement, and therapy from GURPS Horror, pg. 141-146, will be used. (And naturally, GURPS Horror contains is lots of other good material for CoC campaigns as well!) For more realism, the "shell shock" options on pg. 34 of GURPS Tactical Shooting will be used for some Fright Checks, especially those caused by mundane horrors, rather than Sanity-Blasting Mythos effects. [But none of this is vital. You'll do fine with just the Basic Set, if that is all you have.]

Cthulhu Mythos Skill:
Oddly, Hidden Lore is an average skill in 4e, even though it seems to meet the criteria for a very hard skill on B168. I will use The Cthulhu Mythos skill from Cthulhu Lives! instead. This skill does not default to Occultism, as in CthulhuPunk, but some occultists do stumble upon Mythos lore and acquire the skill.

A Mythos tome allows the reader to increase Cthulhu Mythos skill by spending a maximum number of character points equal to half the percentage of skill increase it grants in BRP (round down, minimum 1). [If we assume 99% skill in BRP is equivalent to a skill of IQ+10 in GURPS, this works out about right.]

Whenever characters fail a Fright Check from an encounter with Mythos phenomena and gets a result of 13 or higher, they are entitled to spend one character point on Cthulhu Mythos. Otherwise, they cannot increase this skill without the help of a tome.

Magic:
Spells are IQ/H skills, or VH if they cost more than 12 magic points, and have no Default. They function as in BRP, but read POW as Will, Magic Points as FP+Energy Reserve, and "Resistance Table roll" as "Quick Contest". On a critical failure with a summon/bind spell, the creature appears, but is not bound.

Mythos Creatures:
Some excellent monster write-ups can be found here.

Converting characters from BRP:
The system in Cthulhu Lives! is good for monsters, but it lacks detail for humans. Here are some alternate rules for converting PCs and important NPCs.

Do not reduce IQ by two, as Cthulhu Lives! recommends. Instead, the difference between 10 and the level of any Attribute should be reduced by half, and the Attribute should then be rounded toward 10. This is to account for the facts that BRP Characteristics have less impact on play than GURPS Attributes, and are often quite high or low. (Ignore this rule if the character has a good reason to have an extreme Attribute.) Following are variant options for converting Attributes for humans:

GURPS: BRP
ST: (Str+Siz)/2 (Alternately, use Str for ST! and Siz for HP, if the disparity is small.)
DX: Dex
IQ: (Int+Edu-3)/2
HT: Con (But note that in BRP, "magic points" are based on POW. So to preserve magical power, adjust GURPS FP to equal BRP POW, or give the character Energy Reserve to make up the difference.)
Will: Pow
Per: This is composed of the Listen and Spot Hidden skills. You could average them, or use the lower one for PER and add Acute Sense to model the other. Or use the higher one for PER, and take a Disadvantage that impairs the other sense.

Skill Equivalents (Or, Further Evidence That I have Too Much Free Time):
The skill conversion system in Cthulhu Lives! gives fairly low scores on average (11), and makes skills higher than Attribute+4 impossible. Also, it converts percentages into scores of Att+x, even though Characteristics don't affect skills in BRP. This doesn't agree with me.

In BRP, 50% is the level at which a character can make a living with his skill, and has the maximum chance of succeeding at an easy task. This is probably equivalent to skill 12 or better in GURPS. A character with human maximum skill still fails often in difficult conditions, so no one seems to have a very masterful level of skill in BRP. So 99% should represent 19 or, at best, 20.

Therefore, if we just use the Probability of Success table on B171 (rounding to the nearest whole number), and add 2 or 3 to the scores, we can get reasonable skill levels. If the BRP skill falls between the listed percentages, count it as the lower one. A BRP score of 99% is one level above the top score on the table. For 100%, assign any value you like - this is only used for beings with superhuman abilities.

If the listed level of GURPS skill is lower than a character would have if they spent 1 character point on it, or if no skill points were spent on it in BRP, then they do not have the skill.

Here is the table, using the more generous +3 modifier. This is mainly for PCs and major villains, so I figure we can cut them some slack:

BRP: GURPS
100%: 21+
99%: 20
98%: 19
95%: 18
91%: 17
84%: 16
74%: 15
63%: 14
50%: 13
38%: 12
26%: 11
16%: 10, or what the character would have if he spent 1 cp on the skill, if that would be less.
9%: 9, or a Dabbler Perk for Default +2, if that would be less.
5% or less: Default

I thought about making a conversion from the "How Good Am I?" table on pp.177 of the CoC Keeper's Companion I, but I find it hard to harmonize with the CoC core book, much less GURPS. Still, that table and mine seem to be in the same ball park, at least in part. It equates 35-40% with a bachelor's degree, 40-50% with a master's, and 50-59% with a master's plus practical experience. (And then we go to Fantasy Island, where a Ph.D has a minimum of 60% right out of grad school, with no upper limit. Which is the same as a pro athlete. Right...)

If we ignore the inflated numbers for a Ph.D, I think my table corresponds in a generous but believable manner, as intended. If we subtract 1 from the GURPS skill lvls on my table, and cut the Ph.Ds down to a more plausible 50-65%, I think the correspondence is more realistic.

03-29-2009, 04:59 AM	#42
GodlessRose Join Date: Aug 2004 Location: Cincinnati, OH	Re: Cthulhu in GURPS 4e I'm kind of enthused at the prospect of running CoC with GURPS, even though we haven't played yet. (Had to reschedule the game for next Friday.) I've been looking over the rules and I've typed up some notes. Nothing revolutionary here, but I figure I'll post them for anyone who's interested. I'll be using the rules in Cthulhu Lives!, with the following modifications. Some of these ideas were appropriated from other contributors to this thread, most notably Gollum. (Thanks!) Character Creation: Starting characters are 100 points. Advantages are limited according to Keeping It Real by Paul Blackwell on pg. 31 of issue 3/21 of Pyramid magazine. [This is to make suspense a little easier to maintain, while still allowing players a wide range of character creation options. But if you don't have that issue, don't worry about it. The impact is small, and some would prefer the pulp feel of the standard rules anyway.] The Mythos Awareness Advantage from GURPS CthulhuPunk does not exist. [I don't think it fits the genre.] The Innsmouth Look Disadvantage is tricky to write up and I doubt anyone would want it, so I'll ignore it for now. Fright Checks: When making a Fright Check, refer to the sanity loss for a failed roll in the BRP system. The character receives a penalty equal to (maximum possible die roll)/2, provided the max roll is no more than 24. For higher rolls, the penalty is 10 + (Maximum possible die roll)/10. If a roll has a modifier (e.g., 1d6+1) then double the modifier for this purpose (so 1d6+1 becomes 1d6+2). If the Fright Check is due to a corpse or other mundane cause, however, use the standard GURPS modifiers instead. The rules for Stress, Derangement, and therapy from GURPS Horror, pg. 141-146, will be used. (And naturally, GURPS Horror contains is lots of other good material for CoC campaigns as well!) For more realism, the "shell shock" options on pg. 34 of GURPS Tactical Shooting will be used for some Fright Checks, especially those caused by mundane horrors, rather than Sanity-Blasting Mythos effects. [But none of this is vital. You'll do fine with just the Basic Set, if that is all you have.] Cthulhu Mythos Skill: Oddly, Hidden Lore is an average skill in 4e, even though it seems to meet the criteria for a very hard skill on B168. I will use The Cthulhu Mythos skill from Cthulhu Lives! instead. This skill does not default to Occultism, as in CthulhuPunk, but some occultists do stumble upon Mythos lore and acquire the skill. A Mythos tome allows the reader to increase Cthulhu Mythos skill by spending a maximum number of character points equal to half the percentage of skill increase it grants in BRP (round down, minimum 1). [If we assume 99% skill in BRP is equivalent to a skill of IQ+10 in GURPS, this works out about right.] Whenever characters fail a Fright Check from an encounter with Mythos phenomena and gets a result of 13 or higher, they are entitled to spend one character point on Cthulhu Mythos. Otherwise, they cannot increase this skill without the help of a tome. Magic: Spells are IQ/H skills, or VH if they cost more than 12 magic points, and have no Default. They function as in BRP, but read POW as Will, Magic Points as FP+Energy Reserve, and "Resistance Table roll" as "Quick Contest". On a critical failure with a summon/bind spell, the creature appears, but is not bound. Mythos Creatures: Some excellent monster write-ups can be found here. Converting characters from BRP: The system in Cthulhu Lives! is good for monsters, but it lacks detail for humans. Here are some alternate rules for converting PCs and important NPCs. Do not reduce IQ by two, as Cthulhu Lives! recommends. Instead, the difference between 10 and the level of any Attribute should be reduced by half, and the Attribute should then be rounded toward 10. This is to account for the facts that BRP Characteristics have less impact on play than GURPS Attributes, and are often quite high or low. (Ignore this rule if the character has a good reason to have an extreme Attribute.) Following are variant options for converting Attributes for humans: GURPS: BRP ST: (Str+Siz)/2 (Alternately, use Str for ST! and Siz for HP, if the disparity is small.) DX: Dex IQ: (Int+Edu-3)/2 HT: Con (But note that in BRP, "magic points" are based on POW. So to preserve magical power, adjust GURPS FP to equal BRP POW, or give the character Energy Reserve to make up the difference.) Will: Pow Per: This is composed of the Listen and Spot Hidden skills. You could average them, or use the lower one for PER and add Acute Sense to model the other. Or use the higher one for PER, and take a Disadvantage that impairs the other sense. Skill Equivalents (Or, Further Evidence That I have Too Much Free Time): The skill conversion system in Cthulhu Lives! gives fairly low scores on average (11), and makes skills higher than Attribute+4 impossible. Also, it converts percentages into scores of Att+x, even though Characteristics don't affect skills in BRP. This doesn't agree with me. In BRP, 50% is the level at which a character can make a living with his skill, and has the maximum chance of succeeding at an easy task. This is probably equivalent to skill 12 or better in GURPS. A character with human maximum skill still fails often in difficult conditions, so no one seems to have a very masterful level of skill in BRP. So 99% should represent 19 or, at best, 20. Therefore, if we just use the Probability of Success table on B171 (rounding to the nearest whole number), and add 2 or 3 to the scores, we can get reasonable skill levels. If the BRP skill falls between the listed percentages, count it as the lower one. A BRP score of 99% is one level above the top score on the table. For 100%, assign any value you like - this is only used for beings with superhuman abilities. If the listed level of GURPS skill is lower than a character would have if they spent 1 character point on it, or if no skill points were spent on it in BRP, then they do not have the skill. Here is the table, using the more generous +3 modifier. This is mainly for PCs and major villains, so I figure we can cut them some slack: BRP: GURPS 100%: 21+ 99%: 20 98%: 19 95%: 18 91%: 17 84%: 16 74%: 15 63%: 14 50%: 13 38%: 12 26%: 11 16%: 10, or what the character would have if he spent 1 cp on the skill, if that would be less. 9%: 9, or a Dabbler Perk for Default +2, if that would be less. 5% or less: Default I thought about making a conversion from the "How Good Am I?" table on pp.177 of the CoC Keeper's Companion I, but I find it hard to harmonize with the CoC core book, much less GURPS. Still, that table and mine seem to be in the same ball park, at least in part. It equates 35-40% with a bachelor's degree, 40-50% with a master's, and 50-59% with a master's plus practical experience. (And then we go to Fantasy Island, where a Ph.D has a minimum of 60% right out of grad school, with no upper limit. Which is the same as a pro athlete. Right...) If we ignore the inflated numbers for a Ph.D, I think my table corresponds in a generous but believable manner, as intended. If we subtract 1 from the GURPS skill lvls on my table, and cut the Ph.Ds down to a more plausible 50-65%, I think the correspondence is more realistic. Last edited by GodlessRose; 07-11-2017 at 11:26 AM.