Something I’ve been noticing lately when building NPCs is that although the basis of challenge rating is that a character’s CR is equal to his level, in practice this is often not the case. Wizards of the Coast’s research and development team think the same thing:
The rule that says â€œan nth-level NPC is a CR n monsterï¿½?â€¦ well, letâ€™s just say that the rule isnâ€™t beyond reproach. Itâ€™s true of some classes within some level ranges, but itâ€™s simply not accurate as a general rule. I donâ€™t think any designer will tell you with a straight face that a 1st-level NPC wizard is a good challenge for four 1st-level PCs. (Better hope the NPC gets that sleep spell off, huh?)
One of the reasons is that the character classes are based on the players having them, and the players usually have oodles more magic items than their opponents – they spend almost all of their money on magic items and tend to steal other peoples’ equpiment with alarming regularity. The other reason is that a level 10 wizard is balanced assuming that he will cast his spells gradually over the course of several encounters and that he will do so with the support of the rest of his adventuring party.
At low levels, the formula holds up reasonably well. Compare a level 3 half-orc fighter with a challenge rating 3 ogre. The fighter, assuming generous ability scores, will have 27 hit points, +8 to hit with 2d6+6 damage, an armor class of 20 and saves of +6/+2/+1, with additional feats. The ogre at the same challenge rating will have 2 hit points and on average 2 damage more per hit, with 4 lower AC and a 2 lower Reflex save, and the added benefit of longer reach. The two are sufficiently close.
At high levels, things change. Compare the same fighter at level 11 to the CR 11 cloud giant. The fighter has 83 hit points to the giant’s 178, his AC is still 20 before magic items compared to the giant’s 25, and the fighter’s saves will be +10/+5/+3 against the giant’s impressive +16/+6/+10. The fighter’s improved Strength gives him an attack set of +17/+12/+7 with 2d6+9 damage before magic weapons are considered, but you can be assured that the giant will have a magic weapon improving his existing array of +22/+17/+12 each dealing a fearsome 4d6+18 damage. That’s an average hit of 32 with reach versus the half-orc’s 16 – exactly double. The half-orc, appropriately enough, is half as survivable and half as lethal!
The net result is that as player characters rise in level, human (or humanoid) villains simply aren’t up to the “challenge rating = level” rule, and in the absence of a reliable formula, ought to have their CR determined through ad-hoc ruling. It’s an elephant in the living-room situation where nobody wants to admit that the rule has been inaccurate all along, and so when writing adventures will often either ignore it or find ad-hoc ways to beef up the character. One such adventure had a sorcerer possessed by a demon such that his ability scores were basically all eighteens and he was granted various resistances, in addition to being behind bars. Another made him a ghost and had him effectively “possess” an earth elemental in order that he be survivable enough not to need endless minions, ad-hoc effects and terrain features to protect him.