Giant Rot Grub

Giant Rot Grub

Small Beast Unaligned

AC 14 (Natural Armor + Dexterity)

Hitpoints 44 (8d6+16)

Speed 20 ft

Str 10, Dex 16 (+2), Con 14 (+2), Int 1 (-5), Wis 10 (0), Cha 1 (-5)

Skills Stealth +6

Immunities Charmed, Frightened, Prone

Senses Blind Sight 60′ (Blind beyond this radius)

Passive Perception 10

Languages -

CR 3 (800 xp)

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Actions

Wall Climbing: A giant rot grub can climb a wall at its normal speed without making a climb check.

Burrow into flesh Melee Weapon Attack +4 to hit, reach 5ft,  Hit 3d6 Damage plus Infestation.

Infestation:  A giant rot grub that hits a target immediately burrows into its flesh. The target must make a dc 11 Con save or become infested. A rot grub infestation causes 1d4+1 Con loss each round (DC 11 Con Save ends) until dead. This can be stopped in the first round by the immediate application of fire to the victim’s flesh, or at any time by a cure disease spell. A single giant rot grub can be removed forcibly within a round of attaching, dealing 2d6 points of damage to the victim.

Lost Constitution points return at a rate of 1 per long rest.

Rot Grubs for 5th Edition!

Rot Grub

Tiny Beast Unaligned

AC 12 (dexterity)

Hitpoints 2 (1d4)

Speed 10 ft (-1)

Str 3 (-4), Dex 16 (+2), Con 10, Int 1 (-5), Wis 7 (-2), Cha 1 (-5)

Skills Stealth +4

Immunities Charmed, Frightened, Prone

Senses Blind Sight 30′ (Blind beyond this radius)

Passive Perception 8

Languages -

CR 1/8 (25 xp)

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Actions

Wall Climbing: A rot grub can climb a wall at its normal speed without making a climb check.

Burrow into flesh Melee Weapon Attack +2 to hit, reach 5ft,  Hit 1 Damage plus Infestation.

Infestation:  A rot grub that hits a target immediately burrows into its flesh. The target must make a dc 10 Con save or become infested. A rot grub infestation causes 1d2 Con loss each round (DC 10 Con Save ends) until dead. This can be stopped in the first round by the immediate application of fire to the victim’s flesh, or at any time by a cure disease spell.
Lost constitution returns at a rate of 1 point per full rest a character takes.

Updated 1 Page Monster Creation Reference for 5th Ed.

Changes are Bold

A Creature with a CR below 1 gets 1 free benefit. CR 1-2 Gets 2 Benefits, 3-4 get 4, 5-6 get 6 and so on.
In all cases, round up.
Armor Class
AC = 12.5 + .4* CR
Hit Points
HP = 13.75*CR +10
Speed:
CR/2 points to be spend 1: 30 feet of a given movement type.
Ability Scores
Ability Bonuses 1.33 *CR
Saving Throws
having any saving throw is worth one benefit, as is every 3 points assigned to that saving throw.
Skills
A monster gets 3 + 1*CR skill points for free.
Vulnerabilities
Each thing a monster is Vulnerable to is worth a penalty.
Resistances and Immunities
Each resistance or immunity is worth 1 benefit.
Perception modes:
Normal, Darkvision no cost. Normal 1 penalty to lack
Blindsight, Truesight Costs one benefit to have.
Melee to Hit Bonus
Hit Bonus = 3+ CR/2
Damage
Melee damage is 6 + 2.7*CR
Ranged:
If a creature has no melee attacks, calculate ranged attacks as melee attacks.
If a creature has melee attacks, ranged attacks are one benefit per 3 dmg and 1 per 2 to hit
Abilities This is things like the ability to use a poison, or 5 spell levels of spell casting, or attacks that automatically gain advantage.
Saving throws
If a special ability allows a saving throw, the DC is 10 +CR/4. Count it as a bonus or penalty for every 2 points over under this number.

Compiled Averages: Monsters from Hoard of the Dragon Queen and the Starter Set (I should add the PHB stuff, but maybe later. I’ll probably do that over the month until the next book comes out)

 CR Number XP ac hp speed points total stat bonus points from saves skills vulnerable resistance immunity blind sight dark vision true sight melee hit bonus avgdmg ranged hit points from ranged benefits
0 3 11 4 1.333333 -0.66667 0 0 0 0 0 0 0 0 2 2 0 0 0
0.125 9 13.33333 5.888889 1.222222 -1.44444 0 3 0.222222 0 0.222222 0.111111 0.333333 0 3.555556 4.333333 0.888889 0.222222 0.777778
0.25 14 11.35714 13.5 1.5 -4.14286 0.071429 2.071429 0.214286 0.214286 1 0.142857 0.571429 0 3.5 6.071429 1.142857 0.428571 1.785714
0.5 10 13.6 16.9 1.3 2.1 0 4.2 0 0.6 1.3 0.2 0.4 0 3.8 7.5 2.4 1.2 1.7
1 9 13.22222 26.55556 1.333333 1.888889 0.555556 8.777778 0.111111 0.888889 1.555556 0.666667 0.666667 0 3.555556 8.444444 2 0.888889 2.555556
2 13 12.84615 40.92308 1.846154 1.076923 0.307692 4.615385 0.230769 1.384615 2 0.076923 0.615385 0 4.384615 10.69231 1.538462 0.538462 2.384615
3 9 14.66667 51.33333 1.444444 7.777778 0.333333 4.777778 0.111111 0.888889 1.555556 0 0.777778 0 4.888889 23.11111 1.444444 0.833333 3
4 2 16.5 50 2 5.5 0 5.5 0 3 7.5 0.5 0.5 0 3 9 0 2.5 4
5 6 15.66667 99.83333 6.166667 4.833333 1 3.833333 0.666667 2 2.166667 0.166667 0.833333 0 6.833333 25.33333 0 0 4.666667
6 2 12.5 75 2 4 2 8 0 0 0 0 0.5 0 6 20.5 3.5 0 4.5
7 1 17 126 2 13 5 16 0 0 0 0 1 0 9 38 9 4 4
8 2 16.5 107 3.5 10 5 21 0 0.5 1 0.5 0.5 0 7 21.5 3.5 0.5 8
10 1 17 178 1 1 0 0 0 0 11 0 1 0 10 38 0 0 5
13 2 17 172 4.5 17 8.5 16 2 2 0.5 0.5 1 0 10 35 0 0 12.5
16 1 19 225 6 22 10 17 0 0 1 1 1 0 12 48 0 0 16

A 5th edition Harpy

Harpies are winged humanoids with vicious claws and an ill temper. They are descended from wind spirits, and the winds still come to their aid, protecting them from missile weapons and allowing them to fly with heavy loads. They are often allied with avatars of rage like the Furys and the Eyrines.

 Harpy Medium Monstrous Humanoid CE

——————————————–
AC 14
Hitpoints 55 (10d8+10)
Speed 20ft, Fly 90ft
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Str 10 (0), Dex 18 (+4), Con 12 (+1), Int 10 (0), Wis 12 (+1), Cha 8 (-1)
——————————————–
Skills Acrobatics +6, Sleight of Hand +6
Senses Normal
Condition Immunities: Poisoned
Languages Common
Challenge 4 (450 XP)
———————————————
Special:

Child of the Winds: Any ranged attack against a harpy is made at disadvantage as the winds swirl and gust around her.

 Befouling Presence: Any unattended food or drink within 30′ of a harpy is automatically befouled. This includes magical waters and potions. A character can make a Will save vs DC 13 to keep food and drinks on their person from being ruined. Harpies can consume befouled food and drinks normally.

 

Multi-attack: A harpy can make 2 Claw attacks

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Actions
Claw Melee Weapon Attack +6 to hit, reach 5 ft, one creature. Hit (1d8 + 4) piercing damage.

If a Harpy hits a medium or smaller creature twice in 1 round, she grabs it. The target must make a DC 12 Athletics (Strength) or Athletics (Dexterity) check to escape or the next round she can fly up to 60 feet in the air and drop the target as well as automatically hitting with her regular claw attack. (1d6 bludgeoning damage per 10′).

One Page Quick Reference 5th E Monster Creation Guide

A Creature with a CR below 1 gets 1 free benefit. CR 1-2 Gets 2 Benefits, 3-4 get 4, 5-6 get 6 and so on.
In all cases, round up.
Armor Class
AC = 12.5 + .2* CR
Hit Points
HP = 10.5*CR +9
Speed:
CR/2 points to be spend 1: 30 feet of a given movement type.
Ability Scores
Ability Bonuses 1.75 *CR
Saving Throws
a saving throw is worth one benefit, as is every 2 points assigned to that saving throw.
Skills
A monster gets 3 + 1*CR skill points for free.
Vulnerabilities
Each thing a monster is Vulnerable to is worth a penalty.
Resistances and Immunities
Each resistance or immunity is worth 1 benefit.
Perception modes:
Normal, Darkvision no cost. Normal 1 penalty to lack
Blindsight, Truesight Costs one benefit to have.
Melee to Hit Bonus
Hit Bonus = CR+2
Damage
Melee damage is 4 + 4*CR
Ranged:
If a creature has no melee attacks, calculate ranged attacks as melee attacks.
If a creature has melee attacks, ranged attacks are one benefit per 3 dmg and 1 per 2 to hit
Abilities This is things like the ability to use a poison, or 5 spell levels of spell casting, or attacks that automatically gain advantage.
Saving throws
If a special ability allows a saving throw, the DC is 10 +CR/4. Count it as a bonus or penalty for every 2 points over under this number.

5th edition Monster Creation System Revised and Streamlined

After using it again after not having looked at my monster system for a week and a half, I realized that I needed to pull it out of the analysis. And that some of the numbers could use a bit of tweeking. So here it is with all of the charts and most of the analysis removed:

Creating Monsters:

The first step is to come up with a monster idea and an approximate CR.

Benefits and Penalties: While I give a set of formulae to determine the standard statistics and abilities for creatures of a given CR, if everything fit the average, that would be a bunch of boring monsters. So instead we assign benefits and penalties. A benefit is something that helps a monster or an ability that is stronger than the average for that CR. A penalty is something that harms the monster or is weaker than the average for that CR. Each penalty balances out one benefit. There is space for a couple of benefits that aren’t countered by penalties in each monster, with higher level monsters getting more benefits or powers.

 
A Creature with a CR below 1 gets 1 free benefit. CR 1-2 Gets 2 Benefits, 3-4 get 4, 5-6 get 6 and so on.
 
In all cases, round up.
 

Armor Class
AC = 12.5 + .2* CR
Every 2 points above average is worth 1 Benefit. Every 2 points below average for a CR is worth 1 Penalty. More than 3 Benefits from AC is probably too much.

 

Hit Points
HP = 10.5*CR +9
 

Speed:
Each mode of movement the creature is worth one point. If all of a creature’s movement modes are slower than 20′ per round, that is a penalty. Every 30 feet or fraction thereof higher than 30 feet that a movement type gets is also worth 1 point

A creature gets CR/2 free movement points. Anything beyond that costs benefits.

 

Ability Scores
A creature’s ability score bonuses should total to 1.75 *CR, so if a CR 1 Creature has a Strength of 16, they need a single stat of 8 or 9 to cancel out one point of bonus or they must pay a benefit.

 
Saving Throws
Most monsters don’t get saving throws at all. Having a saving throw is worth one benefit, as is every 2 points assigned to that saving throw.

 

Skills
A monster gets 3 + 1*CR skill points for free.
Lacking any skills is worth 1 Penalty. Every 3 extra skill points is worth on extra benefit.
 

Vulnerabilities
Each thing a monster is Vulnerable to is worth a penalty.
 

Resistances and Immunities
Each resistance or immunity is worth 1 benefit. A creature with a lot of immunities should usually pay for them with penalties in other defensive abilities
 

Perception modes:
Normal No cost to have, 1 penalty for lacking.
Darkvision No cost to have, no penalty for lacking.
Blindsight Costs one benefit to have.
Truesight Costs one Benefit to have.
 

Melee to Hit Bonus
Hit Bonus = CR+2
Bonuses and Penalties are assigned for each 2 point shift from the average.
 

Damage
Melee damage is 4 + 4*CR
This is roughly 1d8+1d8 per level, but different dice expressions that have average damage similar to that work well too. This damage is split between multiple attacks if the monster gets them. Every 4 points over or under is worth a benefit or penalty.
Ranged:

If a creature has no melee attacks, calculate ranged attacks the same way you do melee attacks.

If a creature has melee attacks, ranged attacks are one benefit per 3 points of damage they deal and per 2 points of to hit bonus (so a 3d6 attack with +6 to hit is worth 6 benefits.) This is a good place to fudge a little.
 

Other benefits and Penalties
Benefits
This is things like the ability to use a poison, or 5 spell levels of spell casting, or attacks that automatically gain advantage. If a benefit is particularly strong, make it worth 2 benefits. Don’t worry too much about relative power of abilities unless they are very strong or very weak.
 

Saving throws
If a special ability allows a saving throw, the DC is 10 +CR/4. Count it as a bonus or penalty for every 2 points over under this number.
 

Penalties:
This is things like situational disadvantages, weaknesses, and behaviors that harm the creature.

More Monsters to fill out an old castle.

*edit* I just realized that not only did I build a Kobold  earlier, but the first version was better than the one below. I strongly suggest you use the one at the end of  http://worldmakers.wordpress.com/2014/07/06/monster-math-5th-edition/ instead of what I present here.

Here is a set of monsters that fill in the gaps in the starter set if you wanted to run Castle Caldwell (but not the Dungeons of Terror) from B1-9 In Search of Adventure. We have some traders, an evil cleric of a fire god, a couple of animals and vermin, bandits and their leader, and kobolds! If you use them with the module, remember that in many cases the adventure lists additional behaviors and treasures that are with the monsters.

 

Trader A Medium Humanoid (Human) Neutral
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AC 14 (Studded Leather + Shield)
Hitpoints 18 (3d8+6)
Speed 30 ft
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Str 14 (+2), Dex 10 (+0), Con 14 (+2), Int 10 (+0), Wis 8 (-1), Cha 12 (+1)
——————————————-
Skills Persuasion + 3
Senses Normal
Languages Common, Goblin
Challenge 1 (200 XP)
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Actions
Battle Axe +1 Melee Weapon Attack + 6 to hit, reach 5 ft, one target, Hit: 8 (1d8+3) slashing damage.

 

Trader B Medium Humanoid (Human) Neutral Evil
——————————————-
AC 16 (Chain Mail)
Hitpoints 18 (3d8+6)
Speed 30 ft
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Str 14 (+2), Dex 10 (+0), Con 14 (+2), Int 10 (+0), Wis 8 (-1), Cha 12 (+1)
——————————————-
Skills Deception + 3
Senses Normal
Languages Common, Goblin
Challenge 1 (200 XP)
——————————————-
Special:
Sneak Attack When this trader has advantage, gain 1 extra die of its weapon type in damage.
——————————————-
Actions
Short Sword Melee Weapon Attack + 5 to hit, reach 5 ft, one target, Hit: 6 (1d6+2) piercing damage.

 

 

Trader C Medium Humanoid (Human) Neutral
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AC 16 (Studded Leather + Shield)
Hitpoints 18 (3d8+6)
Speed 30 ft
——————————————-
Str 10 (+0), Dex 14 (+2), Con 14 (+2), Int 10 (+0), Wis 8 (-1), Cha 12 (+1)
——————————————-
Saving Throw Will+1
Senses Normal
Languages Common, Goblin
Challenge 1 (200 XP)
——————————————-
Actions
Longsword Melee Weapon Attack + 4 to hit, reach 5 ft, one target, Hit: 6 (1d8+1) slashing damage.
or
Long Bow +1 Ranged Weapon Attack + 6 to hit, Range 100/600ft, one target, Hit: 7 (1d8+3) piercing damage, 20 arrows.

 

 

Acolyte Medium Humanoid (Human) Neutral Evil
——————————————-
AC 17 (Plate Mail -1 dex)
Hitpoints 15 (3d8 +3)
Speed 30ft
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Str 10 (+0), Dex 9 (-1), Con 12 (+1), Int 10 (+0), Wis 12 (+1), Cha 9 (-1)
——————————————-
Saving Throw Will +2
Senses Normal
Languages Common, Infernal
Challenge 1 (200 XP)
——————————————-
Actions
Spellcasting The Adept is a first level cleric with wisdom as a spellcasting ability. Her spells have a DC 11 Saving throw
and any attack with a spell is at +3 to hit. She may cast 2 first level spells per day.
Cantrips Guidance, Sacred Flame, Thaumaturgy
1st Level Inflict Wounds, Command, Burning Hands (Fire Domain)
Mace + 1 Melee Weapon Attack +4 to hit, reach 5 ft, one target, Hit 3 (1d6) bludgeoning damage
Reaction:
When the acolyte is brought below 5 HP, she drinks a potion during her turn. She possesses 2 healing potions.

 

 

Crab Spider Small Vermin Unaligned
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AC 13
Hitpoints 32 (8d8)
Speed 30ft, Climb 20 Ft
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Str 10 (+0), Dex 16 (+3), Con 10 (+0), Int 1 (-5), Wis 10 (+0), Cha 8 (-1)
——————————————–
Skills Stealth +5
Senses Normal, Blind Sight 30′
Damage Immunities: Poison
Condition Immunities: Blinded, Frightened, Prone, Poisoned
Languages None
Challenge 2 (450 XP)
———————————————
Special:
Spider Climb: The spider can climb difficult surfaces, including upside down on ceilings, without making an ability check.
Surprise Attack: If the Crab Spider surprises a creature, it can drop onto the creature and automatically bite it during the
first round of combat.
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Actions
Bite Melee Weapon Attack +5 to hit, reach 5 ft, one creature. Hit 11 (2d8 + 3 piercing damage and the target must make a DC
12 Constitution saving throw or take 9 (2d8) Poison Damage and gain the Poisoned condition. A creature reduced to 0 HP or less by this poison damage is paralyzed but stable for one hour.

 

 

Bandit Medium Humanoid (Human) Neutral Evil
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AC 12 (Leather Armor)
Hitpoints 13 (3d8)
Speed 30 ft
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Str 14 (+2), Dex 12 (+1), Con 10 (+0), Int 8 (-1), Wis 8 (-1), Cha 10 (+0)
——————————————-
Senses Normal
Languages Common, Goblin
Challenge 1/2 (50XP)
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Special:
Mob Tactics When this Bandit is within 5 feet of an ally, it gains advantage on to hit rolls.
Coward When this Bandit is further than 25 feet from an ally, it is at a disadvantage on to hit rolls.
——————————————-
Actions
Short Sword Melee Weapon Attack + 4 to hit, reach 5 ft, one target, Hit: 6 (1d6+2) piercing damage.

 

 

Bandit Leader Medium Humanoid (Human) Neutral
——————————————-
AC 14 (Studded Leather + Shield)
Hitpoints 18 (3d8+6)
Speed 30 ft
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Str 14 (+2), Dex 10 (+0), Con 14 (+2), Int 10 (+0), Wis 10 (+0), Cha 12 (+1)
——————————————-
Senses Normal
Languages Common, Goblin
Challenge 1 (200 XP)
——————————————-
Special:
For Da Boss once per round, when hit by an attack the Bandit Leader can make a DC 12 Charisma check to cause another bandit to take the attack instead.
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Actions
Longsword Melee Weapon Attack + 6 to hit, reach 5 ft, one target, Hit: 8 (1d8+3) slashing damage.
or
Long Bow Ranged Weapon Attack + 3 to hit, Range 100/600ft, one target, Hit: 4 (1d8) piercing damage, 20 arrows.

 

Giant Shrew, Medium Animal Unaligned
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AC 15 (Hide + Dex)
Hitpoints 40 (8d8 +8)
Speed 30ft, Burrow 10 ft.
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Str 16 (+3), Dex 14 (+2), Con 12 (+1), Int 1 (-5), Wis 10 (+0), Cha 8 (-1)
——————————————–
Senses Blind Sight 60′
Condition Immunities: Blinded
Languages None
Challenge 2 (450 XP)
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Special Abilities:
Furiosity Each round after the first that combat persists, the giant shrew gains an additional +1 to hit and to damage.
Multi-Attack The Giant Shrew may make 2 bite attacks each round.
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Actions
Bite Melee Weapon Attack +5 to hit, reach 5 ft, one creature. Hit 7 (1d8 + 3) piercing damage

 

Fire Beetle Small Vermin Unaligned
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AC 12
HP 20 (3d8+6)
Speed 20 ft, 30 ft Fly
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Str 10 (+0), Dex 10 (+0), Con 14 (+2), Int 1 (-5), Wis 10 (+0), Cha 10 (+0)
———————————————
Senses Normal
Condition Immunities Frightened
Languages None
Challenge 1/2 (50 XP)
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Special Abilities
Glow Gland A fire Beetle can create a soft glow at will. This counts as Normal Light for it and low light for any creature within 30′.
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Actions
Bite Melee Weapon Attack +3 to hit, reach 5 ft, One creature. Hit 4 (1d8) piercing damage.

 

 

Spitting Cobra Tiny Animal Unaligned
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AC 12
HP 9 (2d8)
Speed 20 ft
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Str 8 (-1), Dex 14 (+2), Con 10 (+0), Int 1 (-5), Wis 10 (+0), Cha 0 (+0)
———————————————
Senses Normal
Languages None
Challenge 1/2 (50 xp)
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Actions
Bite Melee Weapon Attack +1 to hit, reach 5 ft, One creature. Hit 3 (1d6) Piercing + target must make a DC 11 Constitution Saving Throw or Take 4 Poison damage and gain the poisoned condition.
Venomous Spit Ranged Weapon Attack +4 to hit, range 5/15 ft, One creature, Hit: Target must make a DC 11 Constitution Saving Throw or Take 4 Poison damage and gain the poisoned condition.

 

 

Kobold Small Humanoid (Kobold) Neutral Evil
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AC 14 (Leather Armor + Dex)
HP 9 (2d8)
Speed 30 Ft
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Str 10 (+0), Dex 16 (+3), Con 10 (+0), Int 11 (+0), Wis 8 (-1), Cha 6 (-2)
———————————————-
Skills
Perception +4
Survival +4
Senses Normal, Darkvision 60′
Languages Common, Draconic
Challenge 1/2 (50 xp)
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Special
Pack Tactics Once per turn a kobold may move 5 feet closer to an ally at the end of his turn.
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Actions
Short Sword, Melee Weapon Attack +5 to hit, reach 5 ft, One creature. Hit 6 (1d6+3) piercing damage.

I release these under a Creative Commons 4.0 BY-SA license
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5th Edition Burning Ghost

A long time ago, I did flavor writeups for a bunch of monsters in a campaign world I am still working on. One of those is the Burning Ghost. Here is a set of stats for the lesser version of this firey undead with bonuses and penalties marked as (+x*) and (-x*) It is at +23* which is what the model presented asks for. If you playtest a burning ghost with your level 4+ D&D party, please let me know how it goes.:
The general description is here http://worldmakers.wordpress.com/2010/11/07/namodesmo-4-burning-ghost/

Burning Ghost, Lesser:
Medium Undead Chaotic Evil
Armor Class 17 (+3*)
HP 63 (9d8+27)
Speed Fly 40 (+1*)
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Str 8 (-1) Dex 18 (+4) Con 16 (+3), Int 10 (0), Wis 14 (+2), Cha 10 (0) (+1*)
——————————————
Damage Resistances Acid, lightning, thunder; bludgeoning, Slashing, piercing from nonmagical silver weapons (+6*)
Damage Immunities Fire, Necrotic, Poison, bludgeoning, Slashing, piercing from nonmagical non-silver weapons (+4*)
Condition Immunities Charmed, Grappled, Paralyzed, Petrified, Poisoned, Prone, Restrained (+7*)
Vulnerabilities Cold, Positive Energy, Force (-3*)
Senses: Passive Perception 12
Languages: Understands languages it knew in life but can not speak in sentences
Challenge 4 1,100xp
——————————————
Incorporeal Movement: A burning ghost can move through an object or creature but may not stop there (+1*)
Burning: A Burning Ghost catches any flammable materials within reach on fire if it stays in one place for more than 1 round. (+1)
Past Life: If a burning ghost is confronted with the type of situation where it burned to death it has disadvantage on attack rolls (-1*)
Contagious Undeath: Any creature burnt to death by a burning ghost rises immediately as a burning ghost (+1*)
—————————————–
Actions
Burning Touch Melee Weapon Attack: +6 to hit. reach 5 ft, one creature. Hit 16(4d8) fire damage and the target must succeed at a DC 14 Reflex save or catch fire, taking 1d6 points of fire damage per round (DC 14 Reflex save or total immersion in water to end) (+2*)

Monster Math 5th Edition

*edit* A lot of these fit log scale plots nicely. That is an artifact of how I am clumping my data. 0, .125, .25, .5, 1, 2, 3, 4 predisposes the data to fit a log scale. If I combined the first 4 categories, we would fit a more traditional linnear curve more often.
*edit 2* I realized I hadn’t included how to set DCs and Saving throws for abilities.

So I took all of the monsters from the D&D starter set, except the dragon whose CR was twice the next lower cr creature and looked at key features of them. For each creature I recorded hp, AC, movement, saves, skills, to hit bonus, average damage of their attacks, ranged hits, average damage of those, and special abilities, including immunities, resistances, perception modes, spell casting, vulnerabilities, etc

Then I treated everything but CR, AC, HP, to hit, and average damage like the * abilities from OD&D.
I broke things into benefits and penalties
Examples of things that gave benefits:

Benefits
Having a saving throw at all.
Each saving throw higher than 3.
Every 3 skill points.
Having extra movement types.
Every 10 feet above 30 movement for the fastest movement type
Having a ranged attack
Every die of damage a ranged attack does past 1.
Having a resistance
having an immunity
having a special perception mode
every 5 levels of spells a spellcaster can cast.
having a situational advantage
gaining extra dice of damage in a given situation.
any other positive ability

penalties
Any vulnerability
having a situational disadvantage
every 10 feet of movement below 20 on the fastest movement type.

Using that, there are on average 3 bonuses plus 5 bonuses per CR on a given creature. If hp or ac is higher than average, aim for fewer bonuses. If they are lower than average then give more bonuses.

For example a cr 1 creature should have a 12 ac and 25 hp and 8 bonuses.
If you give it a 16 AC, you might count that as 2 bonuses (2 AC points per bonus).
Then make it skilled at +3 in 2 skills: 2 more.
Give it a 1d6 ranged attack: 1 bonus
Give it advantage in combat when working with allies: 1 bonus
Give it dark vision (almost everything has dark vision): 1 bonus
Give it a second melee attack 1 bonus
There is a nice CR 1 creature. Some sort of trained and organized warrior, Maybe like a hobgoblin…

Here are all of the charts

CR ac hp # of creatures
0 10 4 1
0.125 13 5 3
0.25 12.25 13.25 4
0.5 15 14 3
1 14 24.8 5
2 11.8 40.6 5
3 13.5 48.75 4
4 13 40 1

The First thing we have is the average number of hit points and the average ac of creatures of a given CR. Notice that we have very small sample sizes and that ACs are falling in a very narrow band. The average AC value moves from about 12.5 to 13 between CR 0 and CR4, so if you give a creature an AC greater than 13 you might want to give it an attendant penalty, or if it has a cr below 12, you might want to give it some sort of bonus.

Approximately 12.5 +.2* CR for the base AC of a creature.

HP are 10.5*CR+9 on average

CR speed points total stat bonus average saving throw skills
0 1 0 0 0
0.125 1.666666667 -4.666666667 0 2.333333333
0.25 1.25 0 0.25 3.25
0.5 1 2.666666667 0 1.333333333
1 1.2 1.6 1 5.4
2 1.4 0.6 0.8 5.2
3 2 7 0 4.5
4 2 3 7

Speed points are based on movement modes. Notice at the lower CRs there is seldom more than 1-1.5 speed point. That means that creatures at those levels should seldom have more than one movement type and should not move more than 30 feet. At CR 3 and 4 though, extra modes of movement and higher speeds are acceptable.

Stat bonuses: I didn’t look at actual ability scores, but at the modifiers they gave. If you ignore the CR .125 and CR 4 entries, you average about 1.75 stat bonus points per CR (this is the sum of positive and negative numbers.) If you include the, it is 1.5 stat bonuses per cr. 1.75x fits the curve better though.

Saving throws are rare. Getting a save at all is worth a bonus, and then give extra saves

Skill points On average everything gets 2.5 skill points and an additional skill point per CR.

Resistances and Immunities

CR vulnerable resistance immunity
0 0 0 0
0.125 0.333333333 0 0.666666667
0.25 0.25 0 1
0.5 0 0 0
1 0 0 0.6
2 0.2 0.8 1.4
3 0.25 2 2.75
4 3 7

Vulnerabilities are something you can hand out whenever you need to balance something else out. They were rare among the set of monsters.

Resistance is pretty rare too, coming in at about 1 resistance per CR > 1

Immunities approximate 1 per CR, though that was often a bunch of creatures immune to nothing and then one or two with several immunities. Notice that the CR4 creature is immune to 7 things, which helps adjust for it having low hp for the CR.

Perception modes:

This doesn’t need a chart. Almost everything has dark vision. most of the rest have blindsight. No truesight was used in the creatures I analyzed.

Combat values

CR melee hit bonus avgdmg points from ranged
0 2 2
0.125 3.666666667 4.333333333 0
0.25 3.75 5 1.5
0.5 4 6.333333333 2.333333333
1 3.2 8.8 1.2
2 3.8 9.4 1
3 4.75 10.75 0
4  5  18 9

So the first question is to hit modifiers. The low cr creatures have really

high to hit modifiers relative to their level. With them in place, you start at +3 and add half a point per point of CR. Without them, it is +2 with .85 points per CR. That second trend line goes almost exactly through CR 0, 1, 2, and 3 (the cr 4 monster has no melee attack.and is mostly a caster, but if you use it ranged attack number the equation is very nearly the same as not including it. (.75*CR+2.25 vs .85*CR+2.0)

So roughly, your creatures should have 2 + their cr in to hit, with a tendency to err on the side of low. If a creature has a to hit number 3 points higher than the average for its cr, that is about the same as giving it advantage and could count as a benefit. If it is 3 points too low, that is roughly the same as disadvantage and should count as a penalty.

Damage:

This has a couple of caveats: If a creature had multiple attacks, I combined their average damages. This is a little inaccurate, but good enough for the accuracy of the data I am working with. It is also balanced by undervaluing multiple attacks. If you look at damage done per round vs a given AC, a second attack is pretty close to doubling the damage if there are no attack penalties. Also, I used WOTC’s damage estimation method. Half the die plus bonuses. The CR4 creature had no melee attack, so i used its ranged attacks. What we get is 3.8 + 3.15*cr damage which is roughly 1d8+ (1d6 per CR). A CR 2 creature thus gets about 10 damage per attack. You can do that as 2d8+2 or 1d8+2d6 or 2 1d8+1 attacks. For every extra die or +3 damage bonus, count that as a benefit, and for each lost die or any minus to damage count it as a penalty.

Ranged

Since ranged attacks are secondary for most creatures, i counted them as pure bonus. The chart isn’t super useful since about 2/3rds of the creatures had no ranged attacks. I assigned them bonus value at a rate of 1 point per die of damage ignoring bonuses and 1 point per 2 points of to hit (round up). So a +5 to hit attack that does 2d8 damage is worth 5 bonus points. It may turn out that in creature creation, that is too many points, but ranged can be a powerful addition.

Other benefits

CR benefits
0 0
0.125 1
0.25 1.25
0.5 1
1 2
2 1.8
3 2.25
4 4

This is things like Poison or 5 spell levels of spell casting or shape changing or attacks with advantage when ambushing. These are the special text block benefits you can give a monster. Remember, bonuses are countered by penalties. (The number on the chart are bonuses not counted anywhere else in the accounting for a monster.)

Oops. I forgot saving throws and ability difficulty classes.

CR average save
0 10
0.125
0.25
0.5
1 11.5
2 12.33333333
3 13
4 13

There were no saving throws between CR 0 and 1. I set CR 0 to 10. There were fairly few data points in the packet. 13 abilities between fewer monsters. I also set the 0 intersect for the trend line by hand to 10 since 10 is the base number. That gives me DC = 10 + .91*CR At CR1 there are creatures with DCs between 10 and 13, so there is a lot of range. My suggestion is if you use a number above the suggested count every 2 points higher as one benefit and every 2 points below the goal as a penalty.So let’s use this system to create a couple of monsters.

 

Kobold

Small and viscous, these doglike humanoids are most comfortable working in packs.

We will start out by assigning a CR.

We’ll make them about equivalent to goblins, so CR 1/4

AC The formula sets it at just over 12, but I imagine them as nasty tenacious beasties, so lets make it 14 which means we have one benefit

HP: Kobolds are weak and easy to kill, the bottom of the food chain in a lot of places. The formula is 10.5*.25 + 9 or about 12. I think we want to go down a bit, say 5 (1d6+2 hp) That is one penalty.

Speed Small and fast, we’ll give them a 30. Great from running away from their natural predators: Everything

Stats:They are pegged at just under one total stat point.Str 6 -2Dex 16 +3Con 14 +2Int 10 +0Wis 8 -1Cha 8 -1

That gives a +1 total to their stats. I think that is fine. No boon or penalty here.

Kobolds are trap makers, and I think they need a save vs their own creations so lets give a benefit in the realm of a Dex+ 0 save.  1 benefit.

________________________________________________________________

So far we are at +2 benefits and -1 penalty.

Skills None

Senses Darkvision 60 feet, passive perception 9  (1 benefit for darkvision)

Languages Common, Kobold.

Challenge 1/4 (50xp)

______________________________________________________________

Cowardly A kobold who is not within 10 feet of another ally is at disadvantage in all to hit rolls(penalty)

Actions:

Pick Axe: Melee Weapon Attack: +2 to hit, reach 5 ft , one target. Hit 3 (1d6) piercing damage.

This is low for a cr.25 creature, 1 penalty.

Poisoned Dart +2 to hit, Range 20ft/80ft Ranged Weapon Attack Hit 1 (1d3-1) + Fortitude DC 10 or gain the poisoned condition (2 benefits)

So we are now at +5 benefits and -3 penalties. That works out to +2 benefits, which is 1 above standard for a cr 1/4.

That is well within the variation in the book, but if you want you can gvie them an extra penalty like:

Light blindness: The first 3 rounds a kobold is in torch light, they gain the blinded condition.

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