5 Monsters by Jack: Room-Sized Mimics, Giant Snakes, Haunted Books, and Worms!

It’s Friday and I’m waiting for tacos to get here (mmm, tacos). While waiting, I asked my six-year-old son Jack for some monster ideas. Here’s what he cooked up:

Idea #1 – Rither

What is a rither?

A monster that changes shape and blends in with everything.

I asked Jack what made the rither different than a doppelganger or mimic. He didn’t really clarify (it more or less sounded like a big mimic), but he explained that the way rithers trick people is different than mimics in that they don’t attack when you get near or touch, rather they wait for you to get inside them.

He used the example of my truck. It’s open, so you go inside, and then CHOMP!

I then offered to Jack, “How about a mimic the size of a room? Once you go inside, it shuts itself off and then uses an enzyme to turn you into treasure.”

His reply? “Cooooollll!”

Idea #2 – Death Snake

What is a death snake?

A giant snake that goblins ride and can swallow people whole.

If you follow this blog, you know how I love weenies and support for weenies. So this one should be pretty fun and easy to do since I can base the snake itself on giant constrictor snakes from the appendix in the Monster Manual.

Idea #3 – Haunted Book

What does a haunted book do?

When you open it it has monsters in it (like your books), and whichever monster you get to, those monsters come to life.

This was a pretty interesting idea that I really liked. Of course, it’s probably better as a cursed magic item than it is a monster, but still, there could be some interesting things here. Sort of like a Deck of Many Things that summons monsters? I played with a few ideas on this one and finally landed on a possessed-book with lich-like powers that can suck creatures inside it. Once the creatures are within, it can expel those creatures as shadows and specters.

Idea #4 – Bloodsucker Worms

What do bloodsucker worms do?

They suck your blood, of course!

Jack’s answer was priceless. Of course, this will work as a swarm. And unlike the rot grub swarm from Volo’s Guide to Monsters that crawls in your flesh and eats your heart (ew), these will drain your blood a la a stirge.




Huge monstrosity (shapechanger), neutral

Armor Class 9

Hit Points 187 (15d12 + 90)

Speed 10 ft.

Abilities Str 25 (+7), Dex 9 (-1), Con 23 (+6), Int 5 (-3), Wis 13 (+1), Cha 8 (-1)

Skills Stealth +7

Damage Immunities acid

Condition Immunities prone

Senses darkvision 120 ft.,

Challenge 11 (7,200)

Shapechanger. The rither can use its action to polymorph into a room measuring up to 15 feet wide by 15 feet long by 15 feet high with one exit (its mouth), or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It reverts to its true form if it dies.

False Appearance (Room Form Only). While the rither remains motionless, it is indistinguishable from an ordinary room. Large or smaller creature can enter the rither’s space.


Pseudopod. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 16 (2d8 + 7) bludgeoning damage. If the target is a creature, it is grappled (escape DC 17) and pulled inside of the rither. The rither can grapple one target at a time with its pseudopod.

Swallow. The rither seals off its exit and collapses in on itself. Any creatures inside of it are swallowed. While swallowed, a creature is blinded, restrained, and has total cover against attacks and other effects outside the rither. At the start of the rither’s next turn, each swallowed creature must make a DC 17 Charisma check or become cursed with the rither’s curse. The cursed target can’t regain hit points, and its Strength score decreases by 1 for every round that elapses. If the curse reduces the target’s Strength to 0, the target dies and its body collapses into a pile of gold coins equal to 10 gold coins for every pound the creature weighs. The curse lasts until removed by the remove curse spell or other magic, the creature exits the rither, or the rither dies. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the rither’s curse for the next 24 hours.

If the rither takes 30 damage or more on a single turn from a creature inside it, the rither must succeed on a DC 16 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 5 feet of the rither. If the rither dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 15 feet of its movement, exiting prone.


Death Snake

Huge monstrosity, unaligned

Armor Class 14

Hit Points 127 (15d12 + 30)

Speed 40 ft., swim 40 ft.

Abilities Str 20 (+5), Dex 18 (+4), Con 14 (+2), Int 7 (-2), Wis 10 (+0), Cha 8 (-1)

Skills Perception +3

Senses blindsight 10 ft., darkvision 60 ft., passive Perception 13

Languages Goblin

Challenge 5 (1,800 XP)


Bite. Melee Weapon Attack: +8 to hit, reach 10 ft. one creature. Hit: 14 (2d8 + 5) piercing damage plus 18 (4d8) poison damage. If the target is a Medium or smaller creature, it is grappled (escape DC 15). While grappled, the creature is restrained until the grapple ends.

Swallow. The death snake makes one bite attack against a Medium or smaller target it is grappling. If the attack hits, the target is also swallowed, and the grapple ends. While swallowed, the target is blinded and restrained, it has total cover against attacks and other effects outside the death snake, and it takes 14 (4d6) acid damage at the start of each of the death snake’s turns. A death snake can have only one creature swallowed at a time.

If the death snake takes 30 damage or more on a single turn from a swallowed creature, the death snake must succeed on a DC 12 Constitution saving throw at the end of tha turn or regurgitate the creature, which falls prone in a space within 10 feet of the death snake. If the death snake dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 15 feet of movement, exiting prone.



Haunted Book

Tiny undead, chaotic evil

Armor Class 15 (18 with mage armor)

Hit Points 99 (18d4 + 54)

Speed 0 ft., fly 40 ft. (hover)

Abilities Str 1 (-5), Dex 20 (+5), Con 16 (+3), Int 20 (+5), Wis 20 (+5), Cha 20 (+5)

Saving Throws Dex +7

Skills Arcana +10, Stealth +10

Damage Vulnerabilities fire

Damage Resistances cold; bludgeoning, piercing, and slashing from nonmagical attacks

Damage Immunities poison, psychic

Condition Immunities blinded, charmed, deafened, frightened, paralyzed, petrified, poisoned, prone

Senses blindsight 30 ft. (blind beyond this radius), passive Perception 15

Languages Common plus up to five other languages

Challenge 15 (13,000 XP)

Legendary Resistance (3/day). If the haunted book fails a saving throw, it can choose to succeed instead.

Magic Resistance. The haunted book has advantage on saving throws against spells and other magical effects.

Rejuvenation. If the haunted book is destroyed, it regains all its hit points in 24 hours unless holy water is sprinkled on its remains or a dispel magic or remove curse spell is cast on them.

Spellcasting. The haunted book is a 17-level spellcaster (spell save DC 18, +8 to hit with spell attacks). It requires no somatic or material components to cast its spells. The haunted book has the following wizard spells prepared:

Cantrip (at will): chill touch, fire bolt, mage hand, message
1st level (4 slots): fog cloud, mage armor, magic missile
2nd level (3 slots): darkness, invisibility, web, shield
3rd level (3 slots): counterspell, dispel magic, lightning bolt, slow
4th level (3 slots): Evard’s black tentacles, stone shape
5th level (3 slots): animated objects, cloud kill, cone of cold
6th level (2 slots): chain lightning, create undead, disintegrate
7th level (1 slot): finger of death
8th level (1 slot): power word stun
9th level (1 slot): power word kill

Turn Resistance. The haunted book has advantage on saving throws against any effect that turns undead.


Trap (Recharge 5-6). The book attempts to absorb into its pages one creature that it can see within 30 feet of it. The target must succeed on a DC 18 Charisma saving throw or become trapped inside the book’s pages. While trapped, the target is incapacitated, it has total cover against attacks and other effects outside the book, and it takes 13 (3d8) psychic damage at the start of each of the haunted book’s turns. In addition, the creature’s hit point maximum is reduced by an amount equal to the psychic damage taken and the haunted book regains hit points equal to that amount. This reduction lasts until the target finishes a long rest. The target dies and is permanently absorbed into the book if this effect reduces its hit point maximum to 0.

If the haunted book takes 30 damage or more on a single turn, the haunted book must succeed on a DC 15 Intelligence saving throw at the end of that turn or eject all living trapped creatures, which fall prone in a space within 10 feet of the haunted book. If the haunted book dies, all creatures are automatically ejected.

Legendary Actions

The haunted book can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The haunted book regains spent legendary actions at the start of its turn.

Cantrip. The haunted book casts a cantrip.

Horrific Imagery (Costs 2 actions). The haunted book flutters, creating frightening images for one creature it can see within 10 feet of it. The target must succeed on a DC 18 Wisdom saving throw against this magic or become frightened for 1 minute. The frightened target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a target’s saving throw is successful or the effect ends for it, the target is immune to the haunted book’s Horrific Imagery for the next 24 hours.

Summon Undead (Costs 3 actions). Up to three shadows or specters appear in unoccupied spaces within 30 feet of the haunted book and remain until destroyed. Undead summoned in this way roll initiative and act in the next available turn. The haunted book can have up to three undead summoned by this ability at a time.



Bloodsucker Worms

Medium swarm of Tiny beasts, unaligned

Armor Class 12 (natural armor)

Hit Points 27 (5d8 + 5)

Speed 20 ft., climb 20 ft.

Abilities Str 3 (-4), Dex 13 (+1), Con 12 (+1), Int 1 (-5), Wis 7 (-2), Cha 1 (-5)

Damage Resistances bludgeoning, piercing slashing

Condition Immunities charmed, frightened, grappled, paralyzed, petrified, prone, restrained, stunned

Senses blindsight 10 ft., passive Perception 8


Challenge 1/2 (100 XP)

Swarm. The swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a Tiny worm. The swarm can’t regain hit points or gain temporary hit points.


Blood Drain. Melee Weapon Attack: +3 to hit, reach 0 ft., one target in the swarm’s space. Hit: 10 (4d4) piercing damage, or 5 (2d4) piercing damage if the swarm has half of its hit points or fewer, and the swarm attaches to the target. While attached, the swarm doesn’t attack. Instead, at the start of each of the swarm’s turns, the target loses 10 (4d4) hit points due to blood loss, or 5 (2d4) due to blood loss if the swarm has half of its hit points or fewer. The swarm can detach itself by spending 5 feet of its movement.


Like Jack’s monsters? Share them!

When I’m low on ideas, Jack’s always got some good ones for me. And he definitely did not fail to deliver this time. I want to use all of these monsters in my own campaign as soon as possible!

Go ahead and click one of the share buttons below. It only takes a minute!

See you next time!


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