What is the most damage that can be done in a single ranged attack?

Question

While we have a question for melee attacks, ranged attacks always seem to get left out.

What is the maximum damage that can be done in a single ranged attack?

• Any official character options as permitted.
• Only official rules should be considered.
• Multiclassing and feats are permitted.
• Magic items from any official source (including adventure modules) are permitted.
  • Additionally, temporary effects from the same sources are permitted.
• Characters can be of any level and are permitted to possess epic boons.
• You are permitted as much setup as required and can assume ideal conditions.
  • This includes things like surprise, target, and location.
• Other characters can assist in the setup, but only one character can be involved in the attack.
• Do not include "Unearthed Arcana".
• Whatever you chose, it must be one ranged attack (i.e. you only perform one attack roll, unless a feature with multiple attack rolls is specifically referred to as one attack).
• Only count damage that is caused by the single attack and occurs in the same round as the attack.

Answer 1

The best I could come up with is 2,084 damage.

• Use an Oathbow (1d8+3d6)

• Drink a Potion of Giant Size from SKT (Oathbow now deals 3d8+9d6)

• Use an Arrow of Slaying (+6d10)

• Have Dexterity 20 then use Dex Tome (+6 dmg)

• Paladin 3 - use Branding Smite (+2d6) also gives you Martial Prof to use the Oathbow

• Rogue Assassin 17 - get "Assassinate" "Death Strike" and 9d6 Sneak Attack. Get Sharpshooter feat while you're at it. (auto-crit and double damage, +9d6 +10)

• Have a Battlemaster Fighter use Commander's strike on you (+1d12)

• Have a Red Dragon Sorc with 22 Charisma cast "Flame Arrows" on you (+4d6 +6)

• Have a Valor Bard cast "Elemental Weapon" on you and give you Combat Inspiration (+3d4 +1d12)

• Have a Paladin cast "Magic Weapon" on you (+3)

• Have a Grave Cleric cast "Holy Weapon" on you and use "Path to the Grave" on the target (+2d8, vulnerability to attack)

• Have a Wizard cast "Enlarge" on you (+1d4)

So that works out to:

• 5d8 + 18d6 + 6d10 + 4d4 + 2d12 = 40 + 108 + 60 + 16 + 24 = 248

• Doubled for critical hit = 496

• Damage bonuses total = +25 = 521

• Double that for Death Strike = 1,042

• Double that for Path to the Grave = 2,084

If you rule that the Potion of Giant Size doesn't increase the Oathbow's extra damage, then the 18d6 becomes 12d6 and the total is adjusted to 1,796.

I don't think there are any other questionable rulings in the calculation.

Answer 2

1296 points of damage

The following setup is used

• Trebuchet 8d10 damage (yes, this counts as ranged weapon, and takes 4 Actions to load and aim, but we're allowed to do this; not sure if you can load something more nasty into a barrel to launch it at the enemy)
  
  DMG, p. 256 (emphasis mine)

  Trebuchet Stone. Ranged Weapon Attack: +5 to hit.

• DEX 20 + 5 x Manual of Quickness of Action (= DEX 30 [+10])

• Commander's Strike by a Battlemaster with a d12 maneuver die
• Sharpshooter +10 damage
• Sneak attack (Rogue level 19+): +10d6 damage
• Crit for doubling the damage dice (Assassinate helps with this)
• doubled damage on a failed DC 24 CON save (Death Strike by Rogue's Assassin archetype) (Use Boon of Fate (DMG) and Bane (PHB spell) to decrease the target's chances of failing the saving throw)
• Contagion (Flesh Rot) (PHB spell) for vulnerability to damage for the target doubling the damage again

$$ 4 \cdot (2 \cdot (8\cdot 10 + 10\cdot 6 + 1 \cdot 12) + 10 + 10) = 1296 $$

The only question here is, if loading and aiming the trebuchet can be done before combat starts. If not, you can still do half this damage ("just" 648 damage)

Using a non magical weapon that is not a siege weapon (heavy crossbow) decreases the max damage by \$7 \cdot 8 \cdot 10 = 560\$. That's still 736 damage without using magical weapons. (Multiply the flat damage dealt by the magic properties by 4 and the damage max damage on the damage dice by 8 to get the effect of a magic weapons/ammunition). In this case you can be sure Assassinate and Death Strike are applicable.