I am in the process of designing an encounter in which a party of 8 level 3 players will fight a group of Chuul.

The CR calculation shows that 3 Chuul will cause a hard encounter, but I intend that the battle have an underwater element.

How does fighting underwater increase the encounter difficulty of a battle?

I will be applying the underwater combat rules as written.

party is made up of Barbarian Artificer Warlock Sorceror Fighter (who mainly uses his bow) Ranger (who mainly uses his bow) Rogue (who mainly uses a bow) Cleric

The idea is that the Chuul are in a pool of water so will swim down and force the players to come to them.

  • 7
    \$\begingroup\$ Please define "underwater element". \$\endgroup\$
    – Mołot
    Jul 12, 2021 at 23:24
  • 3
    \$\begingroup\$ Are you using the rules for underwater combat and no other houserules? What is the party made up of in terms of the number of martials and casters and whether they attack in melee or from a range? \$\endgroup\$ Jul 12, 2021 at 23:27
  • \$\begingroup\$ See my related answer to "How does combat work underwater?". \$\endgroup\$
    – BlueMoon93
    Jul 13, 2021 at 16:27
  • 1
    \$\begingroup\$ I changed CR to “encounter difficulty”, CR is a monster statistic, and the DMG uses encounter difficulty to refer to the overall difficulty of an encounter. \$\endgroup\$ Jul 14, 2021 at 9:32

1 Answer 1


It might increase the difficulty of the encounter one step.

There is some guidance in the encounter design section of the Dungeon Master’s Guide that is relevant here:

Increase the difficulty of the encounter by one step (from easy to medium, for example) if the characters have a drawback that their enemies don’t. Reduce the difficulty by one step if the characters have a benefit that their enemies don’t. Any additional benefit or drawback pushes the encounter one step in the appropriate direction. If the characters have both a benefit and a drawback, the two cancel each other out.

In your scenario, if none of the party have a swim speed, the encounter taking place under water would definitely count as a drawback here for the purposes of estimating encounter difficulty. The Chuul, having a swim speed will find underwater combat to be as easy as combat out of water, your party however, will be at a disadvantage:

When making a melee weapon attack, a creature that doesn't have a swimming speed (either natural or granted by magic) has disadvantage on the attack roll unless the weapon is a dagger, javelin, shortsword, spear, or trident.

A ranged weapon attack automatically misses a target beyond the weapon's normal range. Even against a target within normal range, the attack roll has disadvantage unless the weapon is a crossbow, a net, or a weapon that is thrown like a javelin (including a spear, trident, or dart).

On the other hand, if the party would be mostly unimpeded by fighting underwater (by everyone having a swimming speed), fighting underwater would not affect the encounter difficulty at all.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .