This is my (current) house rule on removing Nat 1 and Nat 20 Auto Fail / Success, but keeping the spirit of it. Is there anything that modifies those circumstances in 1st Party content that won’t mesh well with this house rule?

[Reksew_Trebla]

If, and only if, a nat 1 would auto fail, and/or a nat 20 would auto succeed, it doesn’t, and instead, you roll another d20. You take the number on the extra d20, -19 if it was from a nat 1, or +19 if it was from a nat 20, and that is what you get from the d20. This doesn’t count as a separate roll though, but rather an extension of the original d20. So if you use an ability to reroll a d20 roll, you reroll the original d20, not the second one. For the purposes of things that trigger on a specific nat number being rolled, only the first d20 matters for those triggering.

For instance, you roll a nat 20 on attack, then a nat 1 on the extra die. This results in a 20+attack bonus for the roll. If this would hit, then you get a critical threat. Furthermore, even though you rolled a nat 1 on the second d20, since only the first d20 matters for things that trigger on a specific nat number, you do NOT roll a third d20.

If an ability negates auto failure/success, then it negates the appropriate extra roll.

~~~~~

This makes it where you can roll as low as -18, if a nat 1 would normally auto fail, or as high as 39, if a nat 20 would auto succeed. This is for things to be more realistic, by modifying what I consider an awful mechanic, as there is no way a Kaiju like Mogaru is going to fail to hit a level 1 commoner 1/20th of the time, and there likewise is no way a level 1 commoner is going to hit Mogaru 1/20th of the time.

[yukongil]

I've used -10/+10 for nat 1s and nat 20s since 3rd edition came out.

It was in response to a player with a ridiculous fortitude save failing something like 7 fort saves that they could only miss on a nat 1 in a couple of game sessions, 5 of which resulted in them insta-dying (or wishing it was something as "simple" as death).

That seemed to have been an easy fix for such situations as it really only matters in those niche cases where some extraordinarily powerful being would otherwise have a 5% chance of looking stupid or being hit by people who have no business doing so.

[Quixote]

I don't think Pathfinder is meant to be a perfect reality simulator. If a game includes a combat that involves godzilla and lvl1 commoners as actual participants, something has gone very, very wrong.
A 5% chance to auto fail/succeed is fine when the scenes you set up are appropriate and interesting. If you don't want something ridiculous or silly to happen to the point that it breaks your player's suspension of disbelief (like a housecat confirming a crit on Cthulu or whatever), then don't set up situations where such things can happen?

When you're hacking a game, I think the first thing you have to ask is "how is this enhancing gameplay?" Because "it's more realistic" is not a good enough reason and is absolutely a slippery slope down a very deep rabbit hole.

[Ryze Kuja]

I would argue to keep the current rules in place because your Kaiju scenario is still realistically covered. Even vs. a Kaiju, it is entirely possible that George the Janitor can find a "chink in the armor" so to speak, but chances are high that the Kaiju has DR/Mythic and will ignore most, if not all, of the critical 1d2+str(*2) damage from the Masterwork Mop n Bucket.

Your rule still sounds fine though. I just don't think it's necessary.

[yukongil]

remembering back, it was the massive damage save that kept killing him. Towards the end of the campaign he was pushing high 30's in his Fortitude save but kept dying to natural 1's on the save, cause at that level, nearly every attack caused at least 50 damage. In game, we determined he had a heart condition that every time he raised his arms too quickly (like in a defensive manner when surprised by say a lightning bolt trap) his heart would stop and keel-over he would and then somebody would have to raise dead the cleric...again.

There are some checks, that while sometimes necessary, probably shouldn't ever be failed by specialized characters. Like I don't mind a high level Fighter or even Bard or Monk chucking that 1 on a stealth roll and being spotted by the city guard, but your Batman rogue? Nah, that ain't cool that they are seen 5% of the time

[Quixote]

Well, Massive Damage is an optional rule, and specifically points out the issues with it at higher levels.

And skills do not auto-fail on a 1. That's for attack rolls and saves. So the high level Batman rogue is good to go.

[Zepheri]

I see the natural 1 and 20 rule as a lottery game, those who have all the numbers could say that the jackpot was won natural 20 and those who were not with any good luck with no number is a natural 1

This can provide fun times for bards to tell stories of epic feats or point out anecdotes that shouldn't be done.

[avr]

As mentioned once before, this is basically the Rolemaster open up/open down rolling system. You've changed the way the math operates a little this time but the outcomes are the same.

There are a few odd situations where margins of success matter. These will slightly tend to more extreme results with this house rule; I'm not sure this is a problem, but then I'm not sure 1/20 of the commoners running away surviving Mogaru's AoO is a problem either.