I had a bit of a mental block after I started. Always liked the pic and I could imagine using it (and did - I think - in the 80s). Grey Squaarg and Dragon Warriors could be fun. Trying to think how to shoehorn the cyclops into existing canon....
The main problem with statting the Chthon as a conventional 5E monster is that it is immobile and has no attacks. The only way the original monster could injure its enemies is by siccing its controlled animals and plants on them.
So I'm thinking we might add some attack actions.
The picture shows it looks like a boulder shaped like a splintered tree trunk with a monstrous face on the side, with eyes, nose and a large jagged mouth, which suggests a
Bite attack.
It controls plants as a "defensive screen" so maybe it can animate plants as weapons? Entangling, bludgeoning or crushing enemies with large roots or branches.
Its control ability is overly vague. It can control up to 20 non-intelligent or animal-intelligent plant and animal creatures but the original beast has no restrictions on the power of its minions. It could have anything from a couple of squirrels to a score of mastodons or walking trees at its command, the latter of which would totally crush most opponents.
So I'm thinking its "Nature Allies" should be a more set value. Let's say up to twenty creatures with a total Challenge Rating of 5, so it could be one CR 5 beast or plant such as a giant crocodile or triceratops, a pack of five CR 1 dire wolves, a mob of twenty CR 1/4 or lower creatures like axe beaks, blood hawks or giant rats, or a mixed group that adds up to Challenge 5, like one CR 2 creature plus six CR 1/2 creatures, like an awakened tree plus a half dozen crocodiles.
The SRD includes the following possibilities:
The
Italic Entries appear in the main section of the
Monster Manual while Nonitalic Entries are in
Appendix A: Miscellaneous Creatures (page 317). Unless stated otherwise, the monster's type is beast.
CR 5: dinosaur–triceratops, giant crocodileᵂ, giant sharkᴬ
CR 4: elephant
CR 3: dinosaur–ankylosaurus, giant scorpion, killer whaleᴬ
CR 2: awakened treeᴾ, dinosaur–allosaurus, dinosaur–plesiosaurᵂ, giant boar, giant constrictor snake, giant elk, hunter sharkᴬ, polar bear, rhinoceros, saber-toothed tiger
CR 1: brown bear, dire wolf, gas sporeᴾ, giant hyena, giant octopusᵂ, giant spider, giant toad, giant vulture, lion, myconid–quaggoth spore servantᴾ, tiger
CR 1/2: ape, black bear, crocodileᵂ, giant goat, giant sea horseᴬ, giant wasp, giant wolf spider, reef sharkᴬ, warhorse
CR 1/4: axe beak, boar, constrictor snake, dinosaur–pteranodon, draft horse, elk, giant badger, giant centipede, giant bat, giant frogᵂ, giant lizard, giant poisonous snake, panther, riding horse, violet fungusᴾ, wolf
CR 1/8: blood hawk, camel, flying snake, giant crabᵂ, giant rat, giant weasel, mastiff, mule, poisonous snake, stirge, pony
CR 0: awakened shrubᴾ, baboon, badger, bat, cat, crabᵂ, deer, eagle, frogᵂ, giant fire beetle, goat, hawk, hyena, jackal, lizard, octopusᵂ, owl, quipperᴬ, rat, raven, scorpion, sea horseᴬ, shriekerᴾ, spider, vulture, weasel
ᴬ Aquatic. This creature cannot survive outside the water and is unable to move or fight effectively on land.
ᴾ Plant. This creature has the plant type, other entries are beasts.
ᵂ Water-dweller. This creature normally lives in or near water but can fight on land; it may only be able to survive in air for short periods of time.