D20 Monsters

Load the full format specification from references/stat-blocks.md when detailed guidance is needed.

Quick Reference Tables

Challenge Rating, XP, and Proficiency Bonus

Hit Dice by Size

Creature Types

Aberration, Beast, Celestial, Construct, Dragon, Elemental, Fey, Fiend, Giant, Humanoid, Monstrosity, Ooze, Plant, Undead

Creating a Monster: Step by Step

Step 1: Define the Concept

Determine the creature's narrative role:

• What does it look like?
• How does it fight (brute, skirmisher, caster, support)?
• What makes it interesting or unique?

Step 2: Choose CR and Calculate Base Statistics

Target CR determines the creature's power level. Use these benchmarks:

Step 3: Assign Ability Scores

Distribute scores based on creature role:

Brute (high STR/CON): 16, 14, 14, 10, 10, 8 Skirmisher (high DEX): 10, 16, 14, 10, 12, 8 Caster (high mental): 8, 14, 14, 16, 12, 10 Balanced: 12, 12, 12, 10, 10, 10

Calculate modifiers: (Score - 10) / 2 rounded down.

Step 4: Determine AC and HP

Armor Class:

• Base AC = 10 + DEX modifier
• Add armor bonus (light +1, medium +3-5, heavy +6-8)
• Add shield (+2)
• Natural armor replaces base calculation

Hit Points:

• Choose number of Hit Dice based on desired HP
• HP = (Hit Dice x average per die) + (Hit Dice x CON modifier)

Step 5: Design Actions

Every creature needs at least one attack. Calculate:

Attack Bonus = Ability modifier + Proficiency Bonus Damage = Dice + Ability modifier

For melee: usually STR-based For ranged: usually DEX-based For finesse weapons: attacker chooses STR or DEX

Step 6: Add Special Abilities

Add traits, bonus actions, or reactions that reinforce the creature concept. Common options:

• Pack Tactics: Advantage when ally is adjacent
• Nimble Escape: Disengage or Hide as bonus action
• Magic Resistance: Advantage on saves vs spells
• Multiattack: Multiple attacks per turn
• Spellcasting: Access to spells

Step 7: Validate CR

Compare your creature's statistics to the CR benchmarks. Adjust if the offensive or defensive capabilities don't match the target CR.

Using the Templates

NPC Template

Load references/npc-template.md for a complete template with inline comments explaining each field. Copy the template and fill in values for your creature.

Example Stat Block

Load references/npc-example.md for a complete Goblin Warrior stat block with detailed breakdown of how each value was calculated.

Rolling Dice for HP and Damage

Use the corvran dice-roller skill for randomized values:

# Roll HP for a creature with 3d8 + 6
bash "${CLAUDE_PLUGIN_ROOT}/../corvran/skills/dice-roller/scripts/roll.sh" "3d8+6"

# Roll damage for a longsword attack (1d8 + 3)
bash "${CLAUDE_PLUGIN_ROOT}/../corvran/skills/dice-roller/scripts/roll.sh" "1d8+3"

# Roll 2d6 for greatsword damage
bash "${CLAUDE_PLUGIN_ROOT}/../corvran/skills/dice-roller/scripts/roll.sh" "2d6+4"

The dice roller outputs JSON with the total and individual rolls for narration.

If the dice-roller skill is unavailable, describe the required roll and ask the player to provide the result.

Common Stat Block Patterns

Simple Melee Combatant (CR 1/4)

AC: 13 (leather armor)
HP: 11 (2d8 + 2)
Speed: 30 ft.
STR 14 (+2), DEX 12 (+1), CON 12 (+1)
Attack: +4 to hit, 1d8 + 2 damage

Ranged Attacker (CR 1/2)

AC: 14 (leather armor)
HP: 16 (3d8 + 3)
Speed: 30 ft.
STR 10 (+0), DEX 16 (+3), CON 12 (+1)
Attack: +5 to hit, range 80/320 ft., 1d8 + 3 damage

Tough Brute (CR 2)

AC: 12 (natural armor)
HP: 45 (6d10 + 12)
Speed: 30 ft.
STR 18 (+4), DEX 8 (-1), CON 15 (+2)
Multiattack: Two slam attacks
Attack: +6 to hit, 2d6 + 4 damage

Spellcaster (CR 3)

AC: 12 (15 with mage armor)
HP: 27 (6d8)
Speed: 30 ft.
INT 16 (+3), WIS 12 (+1), CON 10 (+0)
Spellcasting: INT-based, DC 13, +5 to hit
Spells: mage armor, magic missile, fireball (3rd level)

Recording NPCs

After creating a stat block, add it to the adventure's characters.md file for reference during play. Include:

• Full stat block
• Location where the NPC can be found
• Role in the story
• Disposition toward the player

License

This work includes material from the System Reference Document 5.2.1 ("SRD 5.2.1") by Wizards of the Coast LLC. The SRD 5.2.1 is licensed under CC-BY-4.0.