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I'm a new DM, and I'm running through the Starter Set adventure (Lost Mine of Phandelver). At one point, there was an opposed skill check for one of the PC's trying to sneak -- Stealth vs Perception. The player rolled a 20, and there was a bit of discussion about whether that was an automatic success -- similar to Critical Hits.

So, I'm wondering:

  1. Do all opposed skill checks automatically succeed on a natural 20 (unless there's a tie)?
  2. If not all opposed skill checks automatically succeed on a natural 20, do any of them? If so, which ones?
  3. Besides saves & attack rolls, when are natural 20s treated as an automatic success?
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    \$\begingroup\$ Do not answer in comments. \$\endgroup\$
    – mxyzplk
    Jan 12, 2016 at 12:57

3 Answers 3

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Do all opposing skill checks automatically succeed on a natural 20 ( unless there's a tie )?

No, but it's pretty hard for an opponent to beat a natural 20. The opposing roll only ever wins if its total check is higher despite the natural 20. This may happen, say, when a player has a negative modifier to a roll and the opponent rolls high and/or has high scores in the opposing roll.

In one of our games, my 8 strength Lore Bard beat our 18 strength fighter in an arm-wrestling, basically a Strength(Athletics) contest, by picking up Expertise in Athletics, throwing insults at him (Cutting Words Lore Bard feature), and cheating (casting Enhance Ability on myself).

If not all opposing skill checks automatically succeed on a natural 20, do any of them? If so, which ones?

Ability Checks don't have critical success unless house-ruled into your game but I'd be wary of this and that's another topic entirely.

Besides saves & attack rolls, what treats a natural 20 as an automatic success?

Only Attack Rolls treats a natural 20 as a critical hit, even if you roll a natural 20 on a Wisdom Saving Throw, you're still going to be frightened of that dragon if the total doesn't equal or surpass the Save DC.

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    \$\begingroup\$ Note: there are also many house rules on this. For example, in our group, a natural 20 guaranteed an exceptional event. Typically this meant you succeed, but there are plenty of other exceptional results that a clever DM can pull from. (an opposed arm wrestle between a wimp who roles a nat 20 and a strongman who beats him due to a decent roll + modifiers may still lose, but catch the attention of the damsel in the corner, or perhaps the strong man wins but pulls a muscle) \$\endgroup\$
    – Cort Ammon
    Jan 12, 2016 at 6:15
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    \$\begingroup\$ @CortAmmon So something "exceptional" happens 5% of the time? Seems a but unexceptional to me. \$\endgroup\$
    – corsiKa
    Jan 12, 2016 at 21:00
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    \$\begingroup\$ @corsiKa It all depends on how much spice you want in your campaign! Due to utter coincidence, a p-value of 0.05 happens to be a recommended criteria for extraordinary events when rejecting hypotheses, according to Ronald Fisher, the guy who made p-values popular in science back in the early 1900's. I wonder what the odds of that coincidence are ;-) \$\endgroup\$
    – Cort Ammon
    Jan 12, 2016 at 21:15
  • \$\begingroup\$ @CortAmmon: I asked my self "huh? Don't you see Cort Ammon usually just arguing and explaining physics" and then 2 comments further "Ahh, he is it" :D \$\endgroup\$
    – Zaibis
    Aug 25, 2016 at 9:37
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A natural 20 roll has no special meaning for an Ability or Skill Check, whether contested or not. It also has no meaning for a Saving Throw.

Critical Hits only apply to Attack Rolls. They are discussed in the Attack Rolls section in Chapter 9: Combat (page 73 of the Player's Basic Rules). They are not mentioned at all in Chapter 7: Using Ability Scores.

From chapter 9:

If the d20 roll for an attack is a 20, the attack hits regardless of any modifiers or the target’s AC. In addition, the attack is a critical hit, as explained later in this chapter.

However a natural 20 does have a special meaning with regards to Death Saving Throws:

Rolling 1 or 20. When you make a death saving throw and roll a 1 on the d20, it counts as two failures. If you roll a 20 on the d20, you regain 1 hit point.

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  • \$\begingroup\$ Thanks! I don't have the PHB yet, and the basic rules that come with the Starter Kit are pretty sparse. \$\endgroup\$
    – Sean Hagen
    Jan 12, 2016 at 3:53
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    \$\begingroup\$ @SeanHagen You might like to download the free Basic Rules - they cover some areas more thoroughly than the Starter Kit. \$\endgroup\$
    – Adeptus
    Jan 12, 2016 at 4:50
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Criticals are technically only automatic when applied to attack rolls.

This is the correct answer, as indicated in the other answers here.

But....

It is not uncommon for a group to respect the Nat 20 and Nat 1 as auto success / fails, or close to it.

At my table, if a player rolls a nat 20, I give them the best possible result I can without breaking the world.

Example: A PC rolled Nat 20 on his Arcana check some on magical water to know what it would do when he drank it, and I gave him the affirmation that it was magical, and of what school, but that's it. Without an identify spell, or actually drinking it, he couldn't possibly know what would happen.

Criticals are great, they're fun for players and DMs, I like to keep them alive through every aspect of the game in as much as they make sense. That said, auto successes / fails do work a lot better with attacks and saving throws, and are a lot tougher with ability checks and contests because of how varied they are, in application and situation.

A good rule of thumb is not to allow rolls at all for the impossible. But say a character gets bit by a poisonous creature with a DC of 21 and has a -1 to his con check, what a great story moment to pull out a 20 at that moment and succeed against all odds! It's not impossible to pass a DC 21 con check. It would be impossible to say, jump a 1000 ft cavern.

Above all - D&D should be fun. Respect the rules, but find the balance that works for your table.

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  • \$\begingroup\$ I've seen players disrespect this by doing something outrageous like jumping the 1000ft cavern under the guise of nat 20 = success, and rolling without waiting for the DM to adjudicate the circumstances. If you anticipate that as a problem, be sure to talk to your players about what they can expect from a nat 20. Personally - I'd have let the guy get impressively far before he plummeted to his death, but he failed his roll and the GM chose to ignore the player's impulsiveness. \$\endgroup\$
    – Faye
    Nov 3, 2016 at 23:44
  • \$\begingroup\$ The question is asking about contests. For straight ability checks, your answer is valid, but for contests- that's a bit different. \$\endgroup\$
    – daze413
    Nov 4, 2016 at 2:52
  • \$\begingroup\$ I would use the same ruling for contests. \$\endgroup\$
    – Faye
    Nov 4, 2016 at 15:26

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