Secret Lesson 23

Mounted Combat and Underwater Combat

Most combat happens with creatures standing on solid ground.

But adventures can quickly become more unusual.

You might fight:

  • from horseback

  • while riding a fantastic creature

  • while crossing a battlefield on a mount

  • beneath the surface of a lake

  • inside a flooded dungeon

  • in the open ocean

The SRD provides special combat rules for two of these situations:

MOUNTED COMBAT

and:

UNDERWATER COMBAT

These rules modify the normal systems you already know rather than replacing them entirely.

PART ONE — MOUNTED COMBAT

A mount allows one creature to ride another creature during combat.

But not every creature can serve as a mount.

The SRD gives three requirements.

The mount must be:

WILLING

AT LEAST ONE SIZE LARGER THAN THE RIDER

and:

HAVE AN APPROPRIATE ANATOMY

 

THE MOUNT MUST BE WILLING

You cannot automatically use any larger creature as a combat mount.

The creature must be:

WILLING TO SERVE AS THE MOUNT

under the normal mounted-combat rule.

SIZE REQUIREMENT

The mount must be:

AT LEAST ONE SIZE LARGER

than its rider.

EXAMPLE — MEDIUM RIDER

A Medium rider needs a mount of at least:

LARGE SIZE

A Medium creature is not large enough to serve as that rider's mount under the standard rule.

EXAMPLE — SMALL RIDER

A Small rider can use a:

MEDIUM OR LARGER

creature as a mount, provided the other requirements are satisfied.

APPROPRIATE ANATOMY

The creature must also physically be suitable for riding.

The SRD describes this as having:

APPROPRIATE ANATOMY

 

This prevents the Size rule from meaning that every larger willing creature automatically functions as a mount.

The GM applies the creature's physical form and the circumstances.

MOUNTING AND DISMOUNTING

You can mount or dismount a creature:

DURING YOUR MOVE

provided the creature is:

WITHIN 5 FEET OF YOU

 

MOVEMENT COST

Mounting or dismounting costs movement equal to:

HALF YOUR SPEED, ROUNDED DOWN

 

This is movement expenditure.

It is not normally a separate Action.

EXAMPLE — SPEED 30 FEET

Your Speed:

30 feet

Half:

15 feet

Cost to mount:

15 FEET OF MOVEMENT

If you had not moved yet:

Remaining movement from your own Speed:

15 FEET

EXAMPLE — SPEED 25 FEET

Your Speed:

25 feet

Half:

12.5

Round down.

Cost:

12 FEET OF MOVEMENT

YOU MUST BE WITHIN 5 FEET

You cannot spend half your Speed and somehow mount a creature on the opposite side of the battlefield.

The mount must be:

WITHIN 5 FEET

when you mount it.

CONTROLLED VS. INDEPENDENT MOUNTS

Once mounted, a crucial distinction appears.

A mount can effectively function as:

A CONTROLLED MOUNT

or:

AN INDEPENDENT MOUNT

These behave differently in Initiative and combat.

CONTROLLED MOUNT

You can control a mount only if it has been:

TRAINED TO ACCEPT A RIDER

The SRD gives domesticated:

  • horses

  • mules

  • similar creatures

as examples of mounts with that training.

CONTROLLED MOUNT INITIATIVE

When you mount a controlled mount:

ITS INITIATIVE CHANGES TO MATCH YOURS

 

This integrates the mount directly into your turn.

CONTROLLED MOUNT MOVEMENT

A controlled mount:

MOVES ON YOUR TURN AS YOU DIRECT IT

 

So instead of maintaining a separate normal place in Initiative, its movement is coordinated with yours.

CONTROLLED MOUNT ACTIONS

A controlled mount has only three Action options during that turn:

DASH

DISENGAGE

DODGE

 

WHAT A CONTROLLED MOUNT CANNOT NORMALLY DO

Under these standard controlled-mount rules, its available Action choices are limited to those three.

So it doesn't simply gain access to every Action in its stat block while controlled.

Its options are:

Dash

Disengage

Dodge

unless another specific rule changes this.

CONTROLLED MOUNT CAN ACT IMMEDIATELY

A controlled mount can:

MOVE AND ACT ON THE SAME TURN YOU MOUNT IT

 

This prevents mounting from forcing the creature to wait until the next round before functioning.

EXAMPLE — MOUNT AND MOVE

Your Speed:

30 feet

Horse is beside you.

You spend:

15 FEET OF YOUR MOVEMENT

to mount it.

The controlled mount can then:

MOVE ON YOUR TURN

and choose one of its permitted Actions.

DASH WITH A CONTROLLED MOUNT

If the mount takes:

DASH

it gains additional movement according to the normal Dash rules.

This can make mounted characters extremely mobile.

DISENGAGE WITH A CONTROLLED MOUNT

A controlled mount can take:

DISENGAGE

This can be particularly important when moving away from enemies.

Remember:

Disengage prevents the creature's movement from provoking Opportunity Attacks for the rest of the current turn.

DODGE WITH A CONTROLLED MOUNT

A controlled mount can instead take:

DODGE

using the standard Dodge rules.

That may be valuable when:

  • remaining in danger

  • carrying an important rider

  • expecting attacks

INDEPENDENT MOUNT

Some creatures may allow someone to ride them without obeying direct control.

The SRD describes this as an:

INDEPENDENT MOUNT

Such a mount:

RETAINS ITS OWN PLACE IN THE INITIATIVE ORDER

and:

MOVES AND ACTS AS IT LIKES

 

CONTROLLED VS. INDEPENDENT

Mount Type Initiative Movement and Actions
Controlled Changes to match rider Rider directs movement; Actions limited to Dash, Disengage, Dodge
Independent Keeps its own Initiative Moves and acts as it chooses

 

WHY THIS DISTINCTION MATTERS

Consider riding an ordinary trained horse.

You may be able to:

CONTROL IT

Now imagine riding an intelligent or powerful creature that agrees to carry you but acts according to its own decisions.

That creature can remain:

INDEPENDENT

Its turn is not simply absorbed into yours.

FALLING OFF A MOUNT

Mounted combat creates another danger:

FALLING OFF

The SRD provides a specific Saving Throw for several situations.

MOUNT MOVED AGAINST ITS WILL

If an effect is about to move your mount:

AGAINST ITS WILL

while you are riding it, you must make:

DC 10 DEXTERITY SAVING THROW

 

FAILED SAVE

If you fail:

YOU FALL OFF

and land with the:

PRONE CONDITION

in an:

UNOCCUPIED SPACE WITHIN 5 FEET OF THE MOUNT

 

EXAMPLE — MOUNT PUSHED

You are riding a horse.

A magical effect suddenly forces the horse sideways.

The mount is being moved against its will.

Make:

DC 10 DEXTERITY SAVE

Success:

you remain mounted.

Failure:

you fall off and land Prone in an unoccupied space within 5 feet.

IF YOU ARE KNOCKED PRONE WHILE MOUNTED

The SRD says you must make:

THE SAME DC 10 DEXTERITY SAVING THROW

if:

YOU ARE KNOCKED PRONE

while mounted.

IF THE MOUNT IS KNOCKED PRONE

You also make the same save if:

THE MOUNT IS KNOCKED PRONE

 

MOUNTED FALLING CHECK SUMMARY

Make:

DC 10 DEXTERITY SAVE

when:

  • the mount is about to be moved against its will

  • you are knocked Prone while mounted

  • the mount is knocked Prone

Failure:

FALL OFF + LAND PRONE WITHIN 5 FEET

 

MOUNTED COMBAT EXAMPLE

A Medium Fighter rides a trained Large horse.

The horse qualifies because it is:

  • willing

  • at least one Size larger

  • anatomically appropriate

  • trained to accept a rider

The Fighter mounts it.

The horse becomes:

CONTROLLED

Its Initiative matches the Fighter's.

On that turn, the Fighter directs the horse to move.

The horse chooses:

DISENGAGE

Then it carries the Fighter away from nearby enemies without its movement provoking Opportunity Attacks under the Disengage rule.

PART TWO — UNDERWATER COMBAT

Fighting underwater changes how many weapons function.

The SRD gives three major underwater rules:

IMPEDED MELEE WEAPONS

IMPEDED RANGED WEAPONS

FIRE RESISTANCE

 

UNDERWATER MOVEMENT IS NOT THE FOCUS OF THIS LESSON

Swimming movement is governed by the movement rules you learned earlier.

This section focuses specifically on:

COMBAT WHILE UNDERWATER

MELEE WEAPON ATTACKS UNDERWATER

When you make a:

MELEE ATTACK ROLL WITH A WEAPON

underwater, you normally have:

DISADVANTAGE

if you:

LACK A SWIM SPEED

 

IMPORTANT EXCEPTION — PIERCING WEAPONS

The Disadvantage does not apply under this rule if the weapon deals:

PIERCING DAMAGE

 

UNDERWATER MELEE FORMULA

If you lack a Swim Speed:

Weapon deals Piercing damage

NO DISADVANTAGE FROM THIS RULE

Weapon does not deal Piercing damage

DISADVANTAGE

EXAMPLE — SLASHING WEAPON

You are underwater.

You lack a Swim Speed.

You attack with a weapon dealing:

SLASHING DAMAGE

Result:

DISADVANTAGE

 

EXAMPLE — PIERCING WEAPON

You are underwater.

You lack a Swim Speed.

The melee weapon deals:

PIERCING DAMAGE

The underwater melee rule does not impose Disadvantage.

Other circumstances could still impose Advantage or Disadvantage.

SWIM SPEED REMOVES THIS GENERAL MELEE PENALTY

If you have:

A SWIM SPEED

the rule's “lacks a Swim Speed” condition is not satisfied.

Therefore, the standard underwater melee-weapon Disadvantage from this rule does not apply.

THIS RULE SPECIFICALLY SAYS “WITH A WEAPON”

Notice the wording.

The underwater rule specifically addresses:

A MELEE ATTACK ROLL WITH A WEAPON

 

Do not automatically extend that exact rule to every possible melee attack unless another rule says so.

RANGED WEAPON ATTACKS UNDERWATER

Ranged weapon attacks are even more restricted underwater.

The SRD divides them into:

WITHIN NORMAL RANGE

and:

BEYOND NORMAL RANGE

 

WITHIN NORMAL RANGE

If the target is within the weapon's:

NORMAL RANGE

the ranged weapon Attack Roll has:

DISADVANTAGE

 

EXAMPLE

Weapon range:

80 / 320

Target:

50 feet away

50 feet is within normal range.

Underwater result:

DISADVANTAGE

BEYOND NORMAL RANGE

If a target is beyond the weapon's:

NORMAL RANGE

the ranged attack:

AUTOMATICALLY MISSES

 

THIS IS DIFFERENT FROM NORMAL RANGED COMBAT

On land:

Normal range

Attack normally.

Long range

Attack with Disadvantage.

But underwater:

Within normal range

DISADVANTAGE

Beyond normal range

AUTOMATIC MISS

 

UNDERWATER LONG RANGE EFFECTIVELY DISAPPEARS FOR WEAPON ATTACKS

Suppose:

Range 80 / 320

Target:

100 feet away

On land:

100 is within long range.

You could attack with:

DISADVANTAGE

Underwater:

100 feet is beyond the normal 80-foot range.

Result:

AUTOMATIC MISS

under the underwater ranged weapon rule.

DON'T ROLL FOR AN AUTOMATIC MISS

If the target is beyond normal range underwater:

THE ATTACK AUTOMATICALLY MISSES

There is no need to make an Attack Roll hoping for a natural 20.

The specific underwater rule has already determined the result.

UNDERWATER RANGED COMBAT TABLE

Target Distance Result
Within normal range Disadvantage
Beyond normal range Automatic miss

 

THIS RULE SPECIFICALLY APPLIES TO RANGED ATTACKS WITH WEAPONS

Again, the SRD wording says:

A RANGED ATTACK ROLL WITH A WEAPON

 

That distinction matters when later dealing with:

  • spell attacks

  • magical effects

  • special abilities

Use those specific rules rather than automatically applying weapon restrictions to everything.

FIRE DAMAGE UNDERWATER

The final underwater rule is simple but powerful.

Anything underwater has:

RESISTANCE TO FIRE DAMAGE

 

WHAT DOES FIRE RESISTANCE MEAN?

Resistance means the target takes:

HALF DAMAGE

from the relevant damage type after applying the normal Resistance rules.

The full Resistance system belongs to:

LESSON 26

For now:

UNDERWATER → FIRE RESISTANCE

EXAMPLE

A creature underwater would normally take:

18 Fire damage

Because it is underwater and therefore has Fire Resistance:

the damage is reduced according to the Resistance rules.

That concept will be developed fully in Lesson 26.

“ANYTHING UNDERWATER”

The SRD does not limit this rule to:

  • player characters

  • monsters

It says:

ANYTHING UNDERWATER

has Resistance to Fire damage.

So the general rule can also matter for objects and other valid targets when Fire damage is involved.

COMPLETE UNDERWATER MELEE EXAMPLE

Character:

  • no Swim Speed

  • underwater

  • uses a Slashing melee weapon

Attack modifier:

+6

Because the weapon does not deal Piercing damage:

DISADVANTAGE

Roll:

17 and 8

Use:

8

Add:

+6

Total:

14

Then compare to the target's AC.

COMPLETE PIERCING EXAMPLE

Character:

  • no Swim Speed

  • underwater

  • uses a melee weapon dealing Piercing damage

The special underwater melee rule does:

NOT IMPOSE DISADVANTAGE

Make the Attack Roll normally unless another modifier applies.

COMPLETE SWIM SPEED EXAMPLE

Creature:

  • has a Swim Speed

  • attacks underwater with a melee weapon

Because it does not:

LACK A SWIM SPEED

the standard underwater melee Disadvantage does not apply.

COMPLETE UNDERWATER RANGED EXAMPLE

Weapon range:

80 / 320

Target:

60 FEET

Because the target is within:

NORMAL RANGE

the ranged weapon attack can be made, but with:

DISADVANTAGE

SECOND RANGED EXAMPLE

Same weapon:

80 / 320

Target:

150 FEET

On land:

this would be long range.

Underwater:

150 is beyond normal range.

Result:

AUTOMATIC MISS

 

UNDERWATER FIRE EXAMPLE

An underwater creature is hit by an effect dealing Fire damage.

Because:

ANYTHING UNDERWATER HAS FIRE RESISTANCE

the Fire damage is reduced according to the Resistance rules.

MOUNTED COMBAT CHECKLIST

When fighting while mounted, ask:

1. DOES THE CREATURE QUALIFY AS A MOUNT?

Is it:

  • willing?

  • at least one Size larger?

  • anatomically appropriate?

2. ARE YOU CLOSE ENOUGH TO MOUNT IT?

Within:

5 FEET

3. CAN YOU PAY THE MOVEMENT COST?

HALF YOUR SPEED, ROUNDED DOWN

4. IS THE MOUNT CONTROLLED OR INDEPENDENT?

Controlled

Initiative matches yours.

Actions:

  • Dash

  • Disengage

  • Dodge

Independent

Keeps its Initiative and acts as it chooses.

5. HAS SOMETHING THREATENED YOUR SEAT?

If:

  • the mount is forcibly moved

  • you are knocked Prone

  • the mount is knocked Prone

make:

DC 10 DEXTERITY SAVE

to avoid falling off.

UNDERWATER COMBAT CHECKLIST

Ask:

1. IS THIS A MELEE WEAPON ATTACK?

If yes:

Do you have a Swim Speed?

If no, does the weapon deal Piercing damage?

If neither:

DISADVANTAGE

2. IS THIS A RANGED WEAPON ATTACK?

Target within normal range?

DISADVANTAGE

Beyond normal range?

AUTOMATIC MISS

3. IS FIRE DAMAGE INVOLVED?

Anything underwater has:

FIRE RESISTANCE

COMMON BEGINNER MISTAKES

MISTAKE 1 — USING A SAME-SIZE CREATURE AS A STANDARD MOUNT

The mount must be at least:

ONE SIZE LARGER

than the rider.

MISTAKE 2 — FORGETTING THE MOUNT MUST BE WILLING

Size alone isn't sufficient.

MISTAKE 3 — THINKING MOUNTING IS FREE MOVEMENT

Mounting or dismounting costs:

HALF YOUR SPEED, ROUNDED DOWN

 

MISTAKE 4 — LETTING A CONTROLLED MOUNT USE EVERY ACTION

The standard controlled mount has only:

DASH

DISENGAGE

DODGE

as its Action options.

MISTAKE 5 — GIVING AN INDEPENDENT MOUNT THE RIDER'S INITIATIVE

An independent mount:

KEEPS ITS PLACE IN INITIATIVE

 

MISTAKE 6 — FORGETTING THE FALLING-OFF SAVE

Several mounted disruptions call for:

DC 10 DEXTERITY SAVE

 

MISTAKE 7 — GIVING EVERY UNDERWATER MELEE WEAPON ATTACK DISADVANTAGE

The penalty applies when the attacker lacks a Swim Speed unless the weapon deals:

PIERCING DAMAGE

 

MISTAKE 8 — USING NORMAL LONG-RANGE RULES UNDERWATER

For ranged weapon attacks underwater:

BEYOND NORMAL RANGE = AUTOMATIC MISS

not merely Disadvantage.

MISTAKE 9 — FORGETTING DISADVANTAGE WITHIN NORMAL RANGE UNDERWATER

Even within normal range:

RANGED WEAPON ATTACKS HAVE DISADVANTAGE

 

MISTAKE 10 — FORGETTING FIRE RESISTANCE

Anything underwater has:

RESISTANCE TO FIRE DAMAGE

 

LESSON 23 — KEY TAKEAWAYS

A STANDARD MOUNT MUST BE

WILLING

AT LEAST ONE SIZE LARGER

ANATOMICALLY APPROPRIATE

 

MOUNTING OR DISMOUNTING

Creature must be within:

5 FEET

Movement cost:

HALF YOUR SPEED, ROUNDED DOWN

 

CONTROLLED MOUNT

Initiative changes to:

MATCH YOURS

It moves on your turn and can use only:

DASH

DISENGAGE

DODGE

 

INDEPENDENT MOUNT

RETAINS ITS OWN INITIATIVE

and acts as it chooses.

FALLING OFF

Common mounted disruptions require:

DC 10 DEXTERITY SAVING THROW

Failure:

FALL OFF + PRONE

in an unoccupied space within 5 feet of the mount.

UNDERWATER MELEE WEAPON ATTACK

Without a Swim Speed:

DISADVANTAGE

unless the weapon deals:

PIERCING DAMAGE

 

UNDERWATER RANGED WEAPON ATTACK

Within normal range:

DISADVANTAGE

Beyond normal range:

AUTOMATIC MISS

 

FIRE UNDERWATER

ANYTHING UNDERWATER HAS RESISTANCE TO FIRE DAMAGE

 

NEXT LESSON

LESSON 24 — HIT POINTS, DAMAGE ROLLS, CRITICAL HITS, AND SAVING THROWS AGAINST DAMAGE

You now know how creatures attack in ordinary, mounted, and underwater combat.

The next question is:

WHAT HAPPENS WHEN AN ATTACK OR EFFECT HURTS YOU?

In Lesson 24, we will study:

  • what Hit Points represent

  • Hit Point maximum

  • current Hit Points

  • subtracting damage

  • why losing HP normally doesn't reduce your capabilities

  • the Bloodied state

  • damage rolls

  • adding the relevant Ability Modifier to weapon damage

  • fixed damage

  • Critical Hit damage

  • doubling all relevant damage dice

  • additional damage dice such as Sneak Attack

  • damage dealt through Saving Throws

  • rolling damage once against multiple targets

  • half damage on a successful Saving Throw

This begins the Damage and Healing section of combat.

SRD 5.2.1 ATTRIBUTION

This work includes material from the System Reference Document 5.2.1 (“SRD 5.2.1”) by Wizards of the Coast LLC, available at https://www.dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License, available at https://creativecommons.org/licenses/by/4.0/legalcode.