I plan to make a variation of the official NECromancer NPC text block Volo Guide on Monstersand I wanted to make sure the challenge score was correct compared to the original. However, as this is a caster, the calculation of the CR becomes a little weird.
I have done my best to calculate the official necromancer's CR based on health, AC and maximum spell damage, but the CR never seems to reach 9, which is the correct number.
Here is the statistics block of the original necromancer:
Medium Humanoid, All Alignment
Class of armor: 15 (wizard armor)
Points of damage: 66 (12d8 + 12)
Speed: 30 ft
STR 9 (-1)
DEX 14 (+2)
CON 12 (+1)
INT 17 (+3)
WIS 12 (+1)
ACS 11 (0)
Backup throws: Int +7, Wis +5
skills: Arcane +7, History +7
Damage resistances: necrotic
Challenge: 9 (5000 XP)
Spellcasting. The Necromancer is a level 12 caster. His spell casting ability is Intelligence (DC 15 spell save, +7 to launch spell attacks). The necromancer has the following wizard spells:
Cantrips (at will): cold touch, dancing lights, mage's hand, mending
1st level (4 places): false life, * mage armor, radius of illness*
2nd level (3 slots): blindness / deafness, * weakening radius, * the Web
3rd level (3 slots): animate the dead, * spread the curse, * vampiric touch*
4th level (3 slots): rust, * dimension door, stone skin
5th level (2 slots): Bigby's hand, cloudkill
6th level (1 location): circle of death*
* Necromancy of 1st level or higher
Grim Harvest (1 / round). When the necromancer kills a creature that is neither a build nor undead with a level 1 or higher spell, the necromancer regains a health number equal to twice the spell's level or three times if This is a necromancy spell.
Touching withering. Melee attack: +7 touches, reach 5 ft., One creature. Hit: 5 (2d4) necrotic damage.
Can any one explain why this monster has a CR of 9 and how to calculate it?