d20-combat

Combat Management Skill

Use this skill to guide d20-style combat encounters. Combat follows a structured turn order determined by initiative, with each participant taking actions to attack, defend, cast spells, or interact with the environment.

Starting Combat

When combat begins, establish these elements in order:

1. Establish positions - Determine where combatants are located relative to each other
2. Roll initiative - All combatants roll to determine turn order
3. Take turns - Proceed through rounds until combat ends

Rolling Initiative

Each combatant rolls initiative to determine turn order:

Initiative = d20 + Dexterity modifier

Use the mcp__corvran__roll_dice tool for initiative rolls:

Use the mcp__corvran__roll_dice tool:
{ "groups": [{ "n": 1, "d": 20 }], "modifier": 2 }

Order combatants from highest to lowest initiative. Ties between players are resolved by player choice; ties between monsters use GM discretion.

Surprise: If a combatant is surprised (unaware combat is starting), they have Disadvantage on their initiative roll.

Turn Structure

On each turn, a combatant can take the following in any order:

Movement

Move up to your Speed (typically 30 feet). Movement can be split before and after your action.

Action (pick one)

Action	Effect
Attack	Make one attack with a weapon or Unarmed Strike
Cast a Spell	Cast a spell with a casting time of 1 action
Dash	Gain extra movement equal to your Speed
Disengage	Your movement doesn't provoke Opportunity Attacks this turn
Dodge	Attack rolls against you have Disadvantage; DEX saves have Advantage
Help	Give an ally Advantage on their next attack or ability check
Hide	Make a Stealth check to become hidden
Ready	Prepare an action to trigger on a specific condition
Search	Make a Perception, Insight, Medicine, or Survival check
Study	Make an Intelligence check to recall information
Utilize	Use a nonmagical object

Bonus Action

Only available if a feature, spell, or ability grants one. Examples include:

• Two-Weapon Fighting (attack with off-hand weapon)
• Cunning Action (Rogue)
• Certain spells (Healing Word, Misty Step)

Reaction (once per round)

Triggered by specific events. Resets at the start of your next turn.

• Opportunity Attack: When a creature leaves your reach
• Ready: The trigger you defined occurs
• Certain spells: Shield, Counterspell

Free Interaction

One free object interaction per turn (draw a weapon, open a door, pick up an item).

Making Attack Rolls

To attack, roll d20 and add modifiers, then compare to target's Armor Class (AC):

Attack Roll = d20 + Ability Modifier + Proficiency Bonus (if proficient)

Attack Types

Attack Type	Ability Used
Melee weapon	Strength (or DEX with Finesse)
Ranged weapon	Dexterity
Unarmed Strike	Strength
Spell attack	Spellcasting ability

Attack Roll Outcomes

• Roll >= AC: Hit. Roll damage.
• Roll < AC: Miss. No damage.
• Natural 20: Critical Hit. Always hits. Double all damage dice.
• Natural 1: Automatic miss regardless of modifiers.

Use the mcp__corvran__roll_dice tool for attack rolls:

Use the mcp__corvran__roll_dice tool:
{ "groups": [{ "n": 1, "d": 20 }], "modifier": 5 }

Advantage and Disadvantage

• Advantage: Roll 2d20, use the higher result
• Disadvantage: Roll 2d20, use the lower result
• Multiple sources don't stack
• Having both cancels to a normal roll

Common sources of Advantage:

• Attacking while hidden/invisible
• Target is prone (melee attacks)
• Target can't see you
• Help action from an ally

Common sources of Disadvantage:

• Target is prone (ranged attacks)
• You can't see the target
• Ranged attack while enemy is within 5 feet
• Certain conditions (Frightened, Poisoned, Restrained)

Damage Rolls

On a hit, roll the weapon's damage dice plus your ability modifier:

Damage = Weapon Dice + Ability Modifier

Use the mcp__corvran__roll_dice tool for damage:

Use the mcp__corvran__roll_dice tool:
{ "groups": [{ "n": 1, "d": 8 }], "modifier": 3 }

Common Weapon Damage

Weapon	Damage	Type
Dagger	1d4 + modifier	Piercing
Shortsword	1d6 + modifier	Piercing
Longsword	1d8 + modifier	Slashing
Greatsword	2d6 + modifier	Slashing
Shortbow	1d6 + modifier	Piercing
Longbow	1d8 + modifier	Piercing

Critical Hit Damage

Roll all damage dice twice, then add modifiers once:

Critical Damage = (Weapon Dice x 2) + Ability Modifier

Example: Longsword critical = 2d8 + STR modifier

Opportunity Attacks

When a creature you can see leaves your melee reach using its movement, action, or reaction, you may use your reaction to make one melee attack against it.

Avoiding Opportunity Attacks:

• Take the Disengage action
• Teleport
• Be moved by an external force (not your own movement)

Special Combat Situations

Cover

Cover Type	Benefit
Half Cover	+2 AC and DEX saves
Three-Quarters Cover	+5 AC and DEX saves
Total Cover	Can't be targeted directly

Ranged Attacks in Melee

Making a ranged attack while within 5 feet of a hostile creature imposes Disadvantage.

Two-Weapon Fighting

When you take the Attack action with a light melee weapon, you can use your bonus action to attack with a different light melee weapon in your other hand. Don't add your ability modifier to the damage of the bonus attack (unless negative).

Grappling

Use an Unarmed Strike to grapple. Target makes STR or DEX save (their choice) vs DC 8 + your STR modifier + proficiency bonus. On failure, target has the Grappled condition.

Shoving

Use an Unarmed Strike to shove. Same save as grappling. On failure, push target 5 feet or knock them Prone.

Conditions Quick Reference

Combat frequently applies conditions. See references/conditions.md for full details.

Condition	Key Effect
Blinded	Auto-fail sight checks; attacks have Disadvantage
Charmed	Can't attack charmer; charmer has social Advantage
Frightened	Disadvantage on attacks/checks while source visible
Grappled	Speed 0; Disadvantage on attacks vs non-grappler
Incapacitated	Can't take actions, bonus actions, or reactions
Invisible	Advantage on attacks; attacks against have Disadvantage
Paralyzed	Incapacitated; auto-fail STR/DEX saves; auto-crit if hit
Prone	Disadvantage on attacks; melee attacks have Advantage against
Restrained	Speed 0; attacks have Disadvantage; Disadvantage on DEX saves
Stunned	Incapacitated; auto-fail STR/DEX saves
Unconscious	Incapacitated; Prone; auto-fail STR/DEX saves; auto-crit

Death and Dying

Dropping to 0 HP

• Monsters: Die immediately (unless GM rules otherwise)
• Player Characters: Fall unconscious and begin making Death Saving Throws

Death Saving Throws

At the start of each turn while at 0 HP, roll d20:

• 10 or higher: Success
• Below 10: Failure
• Three successes: Become Stable (unconscious but not dying)
• Three failures: Die
• Natural 1: Two failures
• Natural 20: Regain 1 HP and consciousness

Stabilizing

Use the Help action with a DC 10 Medicine check to stabilize a dying creature. A stable creature regains 1 HP after 1d4 hours.

Encounter Templates

For encounter setup and tracking, see references/encounter-template.md and references/encounter-example.md.

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Combat rules derived from SRD 5.2.1, licensed under CC-BY-4.0.