Powers With Progressive Chance of Affliction

[Pursuivant]

How would folks handle a power where repeated or sustained use has a progressively greater chance of triggering some sort of problem, such as burnout (temporarily losing the power) or an Affliction?

For example, a psi has Mind Control, but if they use that power for more than 10 minutes at a time they have a progressively greater chance of suffering Chronic Pain in the form of a migraine which lasts for the rest of the day. While the migraine lasts, they can't use their Mind Control power.

My gut instinct is to create a new modifier based on Temporary Disadvantage and Unreliable, where the cost of the Unreliable limitation is used to determine the mean chance that the power will fail. Initially, the power starts off more reliable than its level Unreliable would indicate, but each cumulative use increases the chance of failure.

For powers which just have a progressive chance of "burning out", use the Limited Use limitation based on maximum possible number of uses and apply some sort of additional limitation.

[Anaraxes]

Start with the value of the Backlash / Nuisance Effect / Temporary Disadvantage Limitation that you'd suffer. Since those are normally guaranteed to take effect, you'd then reduce the value of the Limitation. That is, you're going to Limit the Backlash Limitation. See B111 for the box on "Limited Enhancements", and do the same thing to reduce the value of the Backlash (etc).

How much is of course the tricky part. What's the value of the Limitation for the Limitation?

Mathematically, you could work out the probability of suffering the effect under some assumptions. (If it's an ability you use every turn in combat, and combats usually last up to ten rounds, then you'd have to succeed on the save ten times to avoid the ill effects. If it's a buff you use once at the start of the fight, then it's whatever the probability of a save is.) Of course, failing on turn 5 of that fight means you only suffer the ill effect half the fight, so that's not as bad as failing on turn 1. For that matter, how dire the effect is depends on when it occurs, too. Being paralyzed on round 1 is much worse than being paralyzed on round 10 after the fight in mostly over. (And that observation also depends on whether or not you have some friends along...) ​The ideal calculation is complicated if you try to precisely account for everything that affects the utility of the ability.

It's fairly customary on the forum to treat a variable effect as the average of the costs for the various levels. (The expected value, to be more formal, which means that if your levels of effect aren't of equal probability, you need to weight them by the probability they actually happen.)

1) Requires (Attr) Roll (or "Requires Skill Roll") is a flat -10%, regardless of how good you are at the skill. It assumes you're going buy up that important skill, and the value suggests that you're only going to fail that roll around 10% of the time. But it's not a terrible idea to just go with the first-order probability of "failing" the adverse effect roll as the discount for the Limitation.

2) Do the math on the chain of successes until failure (or estimate it however you'd like), and use Accessibility to convert that "percent of fight expected to be available" number to a Limitation value. (Limitation values aren't probabilities, despite all the times we do math on them as though they were.)

Since you're Limiting a negative value, you might need to use the negated Disad trick, only on the Backlash Limitation value. (See PU8, Limitations, p6, Limitations on Disadvantages, for the logic.)

[maximara]

This topic reminds me of one of the way some fanfics treat the emotional ki techniques of Ranma 1/2.

In those fanficts the more one uses a emotional ki technique the easier it is to feel that emotion which makes it even easier to put off the technique the next time. The downside is the emotion itself becomes an addiction and in some fanfics it becomes the only emotion the user can feel.

[Pursuivant]

Thanks for the feedback.

Originally Posted by Anaraxes

Start with the value of the Backlash / Nuisance Effect / Temporary Disadvantage Limitation that you'd suffer. Since those are normally guaranteed to take effect, you'd then reduce the value of the Limitation.

Using Nuisance Effect/Temporary Disadvantage was my basic plan, but a slight modification to Backlash looks much more promising. Thanks for reminding me that it exists!

Originally Posted by Anaraxes

How much is of course the tricky part. What's the value of the Limitation for the Limitation?

A good approach might be to multiply the larger limitation by (100% - smaller one) and round to the nearest 5%. For example, a -20% limitation on a -40% limitation = 0.4 x 0.8 = .32 = -30%.

Originally Posted by Anaraxes

Mathematically, you could work out the probability of suffering the effect under some assumptions.

I did this to get a "Progressive Risk" limitation using Limited Uses and Unreliable as the base. I figured the average chances on 3d of getting at least 1+n number of uses with a cumulative +1 modifier to the dice roll, compared them to the equivalent level of Limited Uses, applied a flat -5% reduction to that limitation to represent the chance that you get a greater number of uses and filled in the gaps to get a smooth progression.


Progressive Risk
This limitation gives you one guaranteed use of your power. After that, roll the dice applying a +1 modifier per use after the second to see if it fails. A chance of failure which exceeds 15 automatically results in failure. Otherwise, treat it like Limited Uses.

Base Chance of Failure (3d)	Modifier
14	-35%
13	-30%
12	-25%
10	-20%
8	-15%
6	-10%
4	-5%

Originally Posted by Anaraxes

It's fairly customary on the forum to treat a variable effect as the average of the costs for the various levels. (The expected value, to be more formal, which means that if your levels of effect aren't of equal probability, you need to weight them by the probability they actually happen.)

This is what I do, rounding up to the nearest 5%/whole point for advantages, or down for disadvantages.

[Plane]

Originally Posted by Pursuivant

a psi has Mind Control, but if they use that power for more than 10 minutes at a time they have a progressively greater chance of suffering Chronic Pain in the form of a migraine which lasts for the rest of the day.

Maximum Duration: 10 minutes is -50% to start with.

You can use the Either/Or Limitations approach here to propose an alternative to the ability ending at that point.

Backlash: Moderate Pain -20% is halved to -10% if you get a HT roll to resist it.

[Pursuivant]

Originally Posted by Plane

Maximum Duration: 10 minutes is -50% to start with.

You're right, but I was just throwing out an example of a power where a progressive chance of something bad happening makes sense.

Originally Posted by Plane

Backlash: Moderate Pain -20% is halved to -10% if you get a HT roll to resist it.

Modified Backlash is definitely the way to go for any power where there is a chance of something bad happening to the user.

If the risk becomes progressively greater with time, multiply the value of the larger modifier by (100- absolute value of the smaller modifier) Backlash by the value of my Progressive Risk modifier to get the actual cost of the limitation.

For example, a progressive risk of Moderate Pain (no HT roll allowed, -20%) starting at a roll of 12 (-25%) is a limitation worth just (-25% * (100% - 20%) =) -20%.