Level 8 - :) or :(

Nyu is good :)

Don't rush, the damage is high, but the speed is low.

I rarely rush with Necromancers; I usually wait for the opponent to come to me. Death Grip is not available to Knights. Rakshasas are also good, but again, it depends on the circumstances; they also have low initiative and speed.
A Cave Demon, when attacking, can receive damage in return, and Devastating Blow removes positive spells.

I don't see anything useful in them...

I do ;)

And 300 MILITIA are twice as good as 300 PEASANTS; let them stay in the city (and pay taxes; why kill them?)

How often do you encounter 300 militia ready to join you?
And imagine the enemy is in a similar situation? They are in the same position.

The Bone Dragon's growth is the same as everyone else's. You just need to build a Castle and a building that gives +1. If you didn't need to build a Castle, the growth would be 1, not 2.

It's the same, 2 with the Castle, and a building that gives +1, totaling 3.
Green ones have 2.

speed 8, 50% more damage, 200 health, and high initiative, they attack two at once.

Green ones, when biting Bone Dragons, will either receive a curse that lowers their attack or Despair (which is worse). Bone Dragons have 160 health, initiative 11 to 14. Yes, they will arrive and meet the undead.

So, one green one is equal to one and a half Bone Dragons (okay, not two).

Well, there are 3 of them :)

SPECIAL ABILITIES ARE NOT THE REASON FOR THE WEAKNESS OF CREATURES! TRUE LUCK CANNOT BE IGNORED!

The Shriek of Horror also cannot be ignored ;)