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Old 08-09-2019, 02:42 PM   #1
VIVIT
 
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Join Date: Jun 2018
Location: The Wired
Default Alternative Critical Failure Rules

By RAW, a critical failure is any of the following:
  1. A success roll where Roll = 18.
  2. A success roll where TN < 16 and Roll = 17 (if Roll = 17 but TN ≥ 16, the roll is an "automatic" failure, but not a critical failure).
  3. A success roll where RollTN+10.

This seems inelegant to me, particularly the second bit. I understand why it's like that -- if there weren't a special exception for rolls with TNs of 16 and above, then for any such roll, the only possible failure would be a critical failure. Still, the inconsistency of this rule drives my self-diagnosed OCD absolutely bonkers, so I came up with an alternative, similar to the "crit-confirm" rule for games with otherwise static probability of critical success and failure (e.g. only on natural 1s and 20s).
  1. Any success roll where Roll = 17, Roll = 18, or Roll = TN+10 is a critical failure.
  2. After any critical failure, repeat the success roll at an additional penalty of -5. If this second roll is a success, the character has managed to act quickly and avoid disaster, turning the critical failure into an ordinary failure. If it is a critical success, then the character has, through incredible luck and Herculean effort, managed to pull through and turn the critical failure into a success!

I wrote a script to calculate the probability of critical failure both under RAW and under my proposed house rule, and received the following results:
Code:
TN | RAW    | House 
---+--------+-------
3  | 25.92% | 25.44%
4  | 16.2%  | 15.9% 
5  | 9.25%  | 9.08% 
6  | 4.62%  | 4.54% 
7  | 1.85%  | 1.81% 
8  | 1.85%  | 1.81% 
9  | 1.85%  | 1.81% 
10 | 1.85%  | 1.76% 
11 | 1.85%  | 1.68% 
12 | 1.85%  | 1.55% 
13 | 1.85%  | 1.37% 
14 | 1.85%  | 1.15% 
15 | 1.85%  | 0.92% 
16 | 0.46%  | 0.69% 
17 | 0.46%  | 0.48% 
18 | 0.46%  | 0.3%  
19 | 0.46%  | 0.17% 
20 | 0.46%  | 0.08% 
21 | 0.46%  | 0.03% 
22 | 0.46%  | 0.03% 
23 | 0.46%  | 0.03% 
...
Note that the probability of critical failure decreases with almost every step rather than only doing so when there is a risk of a margin of failure of 10 or more and at the transition from TN 15 to TN 16. This means that a TN of 17 is actually better than a TN of 16 for reasons other than an improved margin of success! It's not much, but it's something.

This house rule does require you to make more success rolls, but on average only about 1.85% more.

In short, the house rule simplifies the rules for critical hits and makes it so that increasing the TN usually makes critical failure less likely rather than only doing so as an edge case, yet keeps all probabilities in the ordinary range of target numbers mostly the same as they were before.

Thoughts?
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