Also, so people understand my CR guidelines. This is how I understand certain CRs and CR ranges.
Challenge Rating Guidelines
CR 0 - easily to moderately defeated by normal people, examples commoners, cats, badgers, single rodents,
CR ⅛ - slightly stronger than a normal person, examples bandits, cultists, dolphin, guards, dogs, mules
CR ¼ - decently stronger than a normal person and likely to win in a 1v1, examples boar, wolf, acolyte, constrictor snake, cow, horse, elk, flying sword
CR ½ - capable of defeating small groups of normal people and easily defeating CR ⅛, examples crocodile, gazer, orc, reef shark, scout, swarm of insects, thug, warhorse
CR 1 - too strong for a normal person to defeat without help and equipment, capable of defeating small groups of bandits, examples bear, animated armor, dire wolf, dryad, ghoul, harpy, tiger
CR 2 - 3 - strong enough to be a sizeable threat to a village or small town, examples bandit captain, blue and black dragon wyrmlings, knight, druid
CR 4-6 - notable threats to medium sized towns, strong enough to become tall tales for those who have never seen them. Examples, brontosaurus, allip, animated breaths, barbed devils, cyclops, ettin
CR 7-9 - individuals of great ability or creatures capable of destroying large towns, examples, assassin, blackguard, bone devil, fire giant, giant ape, champion
CR 10 -13 - creatures of near legend, respected or feared, able to defeat small armies of people, capable of controlling or destroying small to medium sized cities, examples adult copper, topaz, white dragons, archdruid, archmage, behir, beholder, deva, genies, erinyes, kirin, roc, storm giant
CR 14 - 17 - the smallest of legends, creatures of enough power to affect entire countries with their power and/or influence, examples adult silver dragon, cadaver collector, death knight, death tyrant, elder brain, goristro, ice devil, marilith
CR 18 - 22 - legendary creatures powerful enough to destroy armies and siege cities in a day, only the strongest of people can reliably defeat these creatures, examples, most ancient dragons, balor, demilich, lich, pit fiend, red abishai, solar
CR 23 - 26 - fantastic legendary beings, tales of their might will stay for ages, only the greatest of armies and heroes can hope to defeat these beings, examples the strongest ancient dragons, arch fiends, empyrean, marut, kraken, gem greatwyrm
CR 27 - 30 - woe is the fool who angers these creatures, mighty beyond all measures, no creature before can defeat them, and even the greatest of heroes and armies will likely fall at their feet, examples, chromatic and metallic greatwyrms, divine avatars, tarrasque
This only takes into account official monsters and their CR. Some creatures may be more powerful narratively of course. The Noble is a great example of this, as a CR 1/4 it is little to no threat against a even low level party in combat, but its narrative capability is far greater than many monsters far stronger than it.
