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If you are rolling with disadvantage and roll a natural 20 on one of those rolls, which die roll do you take?

My question stems from the fact that natural 20s count as critical regardless of modifiers, but disadvantage means you take the lower of the two rolls.

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The rule on modifiers applies only after you've determined a base roll. And to do that you must first resolve disadvantage (PHB page 173):

Use the higher of the two rolls if you have advantage, and use the lower roll if you have disadvantage.

Therefore, you always take the lower roll.

This is a direct inverse of this answer here for rolling a critical miss with Advantage.

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  • \$\begingroup\$ Beat me to it! +1 :) \$\endgroup\$ – Meta4ic Dec 10 '15 at 14:50
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You have to take the lowest roll when you have disadvantage (as mentioned by DaFluid). So you have a critical hit only if you roll two 20, which is rather unlikely, obviously.

You may calculate the likelihood: since you have 5% to roll a 20 (1 / 20 = 0.05), you have 0.05 * 0.05 = 0.0025, or 0.25% of rolling two 20 when rolling an attack with disadvantage.

Note that there are some classes and feats that give you the possibility to get a 19 or a 20 and have a critical hit. In that case, you increase your chances by ×4 since you may get any of (20, 20), (19, 20), (20, 19), or (19, 19) to get a critical hit. So 1% chance instead of 0.25%.

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  • \$\begingroup\$ Good information and +1, but the statistics are kinda superfluous. :-) \$\endgroup\$ – Escoce Dec 10 '15 at 21:26
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    \$\begingroup\$ I thought the stats gave a better idea of how your chances of getting a critical hit are. 5% → 0.25% is quite a drop! \$\endgroup\$ – Alexis Wilke Dec 11 '15 at 2:21
  • \$\begingroup\$ Oh it's good info, no doubt. Just wasn't part of what I am asking. \$\endgroup\$ – Escoce Dec 11 '15 at 2:30
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    \$\begingroup\$ As odd as it sounds, the answers are meant to help many people and not only who asks the question. That's the point of StackExchange. So, more information there are in an answer, the better. \$\endgroup\$ – STT LCU Dec 11 '15 at 8:56
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2. Determine modifiers. The DM determines whether the target has cover and whether you have advantage or disadvantage against the target. In addition, spells, special abilities, and other effects can apply penalties or bonuses to your attack roll. (PHB p. 194, "Making an Attack")

Rolling 1 or 20

Sometimes fate blesses or curses a combatant, causing the novice to hit and the veteran to miss. If the d20 roll for an attack is a 20, the attack hits regardless o f any modifiers or the target’s AC. In addition, the attack is a critical hit, as explained later in this chapter. (PHB p.194, "Attack Rolls")

If the d20 roll for an attack is a 1, the attack misses regardless of any modifiers or the target’s AC.

advantage and disadvantage are modifiers and therefore ignored with natural 20's and natural 1's

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  • \$\begingroup\$ Welcome to RPG.SE! Please take a look through the tour( rpg.stackexchange.com/tour) when you get the chance. I think the issue here is that the natural 20/1 rules only apply to attack rolls, whereas reliable talent covers skill checks. There's no auto-fails on skills. Additionally, Advantage and Disadvantage are not defined as modifiers, so criticals wouldn't override them. \$\endgroup\$ – UrhoKarila Oct 7 '16 at 16:04

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