---
name: d20-monsters
description: This skill should be used when the GM needs to create NPCs or monsters, generate stat blocks, determine enemy stats, design creatures, or generate adversaries for d20-style RPG encounters. Provides SRD 5.2 stat block format and NPC templates.
version: 1.0.0
---

# Monster and NPC Creation Skill

Create monsters, NPCs, and adversaries using the SRD 5.2 stat block format. This skill provides the standard format, reference tables, and templates for generating balanced creatures.

## When to Use This Skill

This skill applies when:
- Creating a new monster or NPC for an encounter
- Converting a narrative concept into game statistics
- Generating stat blocks for adversaries
- Balancing creatures for specific Challenge Ratings
- Looking up stat block format requirements

## Stat Block Format Overview

Every creature stat block follows this structure:

1. **Name and General Details**: Name, size, type, tags, alignment
2. **Combat Highlights**: AC, HP (with hit dice), Speed, Initiative
3. **Ability Scores**: Six abilities with scores, modifiers, and saves
4. **Additional Details**: Skills, resistances, immunities, gear, senses, languages, CR
5. **Traits**: Passive or conditional special abilities
6. **Actions**: What the creature does on its turn
7. **Bonus Actions**: Quick actions (optional)
8. **Reactions**: Triggered responses (optional)
9. **Legendary Actions**: For powerful creatures (optional)

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

## Quick Reference Tables

### Challenge Rating, XP, and Proficiency Bonus

| CR | XP | PB | CR | XP | PB |
|----|----|----|----|----|-----|
| 0 | 10 | +2 | 6 | 2,300 | +3 |
| 1/8 | 25 | +2 | 7 | 2,900 | +3 |
| 1/4 | 50 | +2 | 8 | 3,900 | +3 |
| 1/2 | 100 | +2 | 9 | 5,000 | +4 |
| 1 | 200 | +2 | 10 | 5,900 | +4 |
| 2 | 450 | +2 | 11 | 7,200 | +4 |
| 3 | 700 | +2 | 12 | 8,400 | +4 |
| 4 | 1,100 | +2 | 13 | 10,000 | +5 |
| 5 | 1,800 | +3 | 14+ | See stat-blocks.md | +5 to +9 |

### Hit Dice by Size

| Size | Hit Die | Avg HP/Die |
|------|---------|------------|
| Tiny | d4 | 2.5 |
| Small | d6 | 3.5 |
| Medium | d8 | 4.5 |
| Large | d10 | 5.5 |
| Huge | d12 | 6.5 |
| Gargantuan | d20 | 10.5 |

### 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:

| CR | HP Range | AC | Attack Bonus | Damage/Round | Save DC |
|----|----------|-----|--------------|--------------|---------|
| 1/4 | 10-20 | 12-13 | +3 to +4 | 4-5 | 10-11 |
| 1 | 25-45 | 13-14 | +4 to +5 | 9-14 | 12-13 |
| 5 | 80-110 | 15-16 | +6 to +8 | 35-45 | 14-15 |
| 10 | 180-220 | 17-18 | +9 to +10 | 65-75 | 17-18 |

### 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 mcp__corvran__roll_dice tool for randomized values:

**Roll HP for a creature with 3d8 + 6:**
```
Use the mcp__corvran__roll_dice tool:
{ "groups": [{ "n": 3, "d": 8 }], "modifier": 6 }
```

**Roll damage for a longsword attack (1d8 + 3):**
```
Use the mcp__corvran__roll_dice tool:
{ "groups": [{ "n": 1, "d": 8 }], "modifier": 3 }
```

**Roll 2d6 for greatsword damage:**
```
Use the mcp__corvran__roll_dice tool:
{ "groups": [{ "n": 2, "d": 6 }], "modifier": 4 }
```

The tool returns JSON with the total and individual rolls for narration.

## 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.


---
Source attribution: rjroy
Original project: https://github.com/rjroy/adventure-engine-corvran/blob/72950a82d881d43fef774860caf694fecaec8e2c/plugins/d20-system/skills/d20-monsters/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Dave AI.

## Upstream license notice

MIT License

Copyright (c) 2025 Ronald Roy

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Dave AI resource metadata

Creator / publisher: rjroy
Original project: https://github.com/rjroy/adventure-engine-corvran/blob/72950a82d881d43fef774860caf694fecaec8e2c/plugins/d20-system/skills/d20-monsters/SKILL.md
Attribution basis: Recovered original package and original project license at a pinned revision

Fields of work: Development & Engineering
Roles: Game Developer
Specialties: Specialty not specified
Tools: Tool not specified
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 28aca6f64b7516ad22b0fe27627e8bc023302d27d983e3feeb548c9835221bc9
Metadata reviewed: 2026-10-27
This metadata supersedes earlier Dave AI catalog attribution. Original instruction and supporting files are preserved.