Okay, now for the tricky bit. It's
Control Animals and Plants ability.
Here's a first stab at it.
Control Animals and Plants. The chthon can telepathically control nonsapient flora and fauna. A single chthon can control up to twenty beasts and plants of Intelligence 0 to 3 [?] whose total Challenge Rating adds up to 3 [?] or less.
The chthon may try to establish control over any beast or plant within 60 [?] feet which does not have a special link to another creature (it cannot control a ranger's animal companion or a plant animated by a druid's spell, for example). The target must succeed at a DC 13 Charisma [or Wisdom?] saving throw or fall under the chthon's control, which lasts until the chthon releases the controlled creature (a free action), the chthon or the creature are dead or unconscious, the two are separated by more than a mile, or the creature is affected by a power that breaks mind control. Controlled creatures always seek to remain within 1 mile of the chthon.
If a controlled beast or plant is within 120 [?] feet, the chthon can send it telepathic orders the creature follows to the best of its natural ability. The chthon cannot force a controlled creature to do anything it could not do normally, such as suicidal or unnatural actions.
The chthon can telepathically call any or all creatures under its control to come towards the chthon and receive orders. This call has a range of 1 mile.
It also seems to be prudent to include a note as to how the animal allies & Chthon's CR combine, i.e.:
Note (inclusive): The chthon's Challenge of # include a Challenge # retinue of controlled beasts and plants.
Note (exclusive): The chthon's Challenge of # does not include its retinue of controlled beasts and plants.
My original draft used a Challenge 5 total, but upon reflection that seemed too much. That's twenty wild boars or ten giant wolf spiders. Challenge 3 allows, say, a giant boar or allosaurus plus four giant wolf spiders, a dozen boars, or 20 giant rats. Those seem way more manageable encounter sizes.
