That's kind of irrelevant though. Whether it's an auto-crit or fail doesn't matter when dude rolled as low as you possibly can. Might not be an autofail at most tables but it might as well be because chances are that this person didn't meet the minimum roll required.
Very much depends on the modifier, though. Like in Baldur's Gate 3 they do crit fails/successes which is what made me think of this. But say my character is a level 20 wizard with an essentially superhuman mastery of Arcana. So a bonus of +12 to arcana and is presented with a rune that needs to be identified:
Under the crit fail/success system, this genius Archmagus with a knowledge of Arcana in the same ballpark as Mystra herself has a 5% chance of not knowing what the fuck that rune does instead of whatever small percentage rolling a minimum of 13 would get you on that particular skill challenege. If this dude rolled the lowest he can roll, it is and should still be treated as pretty damn good.
And it's ultimately up to the DM, of course, but RAW matters too
BG3's crit fails on skill checks drive me crazy. I have failed so many DC 10 sleight of hand checks because of that natural one. Like, easily 1/3, despite it supposedly being a 5% chance
Exactly! That's what I love! Consequently, it's also the one thing about Baldurs Gate 3 that I think is genuinely bad and very short sighted. There have been countless checks I've failed in that game because of that whole "autocrit/autofail" thing. It doesn't make any sense. You build a character to be good at a thing so that the minimum they can do is still better than anyone else but you have a perpetual 5% chance of catastrophic failure? No. Fuck that.
I don't run autochecks and autofails and I never will because I want my players to feel like their build actually matters.
in 2e, its a pretty big difference. A failed stealth check bumps down your stealth status to "Hidden" (What was that noise? Who's footprints are these? etc.), while a crit fail makes you full on "observed" (Tony Tony Chopper style.)
The Assurance: Stealth feat is the lynchpin in many a clunky fighter's exploration kit, since it will pretty much never critically fail, giving them time to hide somewhere or get help from a sneakier friend.
Sort of since what the DM says ultimately goes, but no - a crit fail means your effort just fails no matter what. Now, it may also mean that your acrobatics check ends in you slipping on a banana peel and breaking your back, but it doesn't have to be dramatic.
So, crit fail means that no matter how skilled you are, you have a 5% chance of failing anything you attempt (without advantage, lucky, etc. anyway)
Does the DM 'have' to make it worse than a normal fail? I know some swear by it, but I've never actually looked if it's any written rule or suggestion.
No not at all - it's just fun to. A nat one on attacks always misses though. Some DMs say if you nat one your attack you might hit a teammate or do something else disadvantageous, but it's all contextual.
Plenty of people do, it sucks. Nothing like having a bonus large enough to still pass even on a one but because someone likes more critical failures you fuck up at doing something that should be comically mundane to your supposed expert 5% of the time.