For PCs, cantrip damage increases with their total character level and not their class level (see this question for reference).
However, NPCs do not normally have class levels, and their stat blocks don't state a total character level.
How can I determine the number of damage dice to roll for an NPC's cantrip?
- Should I use their number of hit dice as their total character level?
- Should I use their stated Spellcaster level? (What if they don't have one?)
- Some other method?
A couple of examples to illustrate my concern:
- An Archmage (SRD p. 395) has 18d8 + 18 hit dice and is an 18th level spellcaster, so methods 1 & 2 here would produce the same result.
Nezznar the Black Spider (LMOP p.59) has 6d8 hit dice and is a 4th level spellcaster, so methods 1 & 2 would produce different results.
The fact that Nezznar has more hit dice than spellcasting levels implies to me that Nezznar has, in some unspecified way, multiclassed - and that 6 would be his total character level - and the number I should use for cantrips, not 4 (his spellcasting level).
A good answer would also cover NPCs with Innate Spellcasting and no spellcasting level. See for instance:
- A Green Hag (SRD. p 319) has 11d8 + 33 hit dice but no spellcasting level.