How is cantrip damage determined when cast by NPCs?

Question

A Green Hag (MM, p. 177) has an Innate Spellcasting trait that includes the spell vicious mockery. The description of the vicious mockery cantrip states, in part:

[The target] must succeed on a Wisdom saving throw or take 1d4 psychic damage and have disadvantage on the next attack roll it makes before the end of its next turn.

This spell's damage increases by 1d4 when you reach 5th level (2d4), 11th level (3d4), and 17th level (4d4).

I heard somewhere that the amount of hit dice in NPCs is used as their level. A green hag has 82 (11d8 + 33) hit points. So does vicious mockery do 3d4 psychic damage on a failed save when cast by a green hag?

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score 37 · Accepted Answer · edited Nov 11 '21 at 20:11

37

Use Challenge Rating.

The introduction to the Monster Manual has a rule on page 10, under "Innate Spellcasting":

[...] If a monster has a cantrip where its level matters and no level is given, use the monster’s challenge rating.

You can also read this section here in the Basic Rules.

So a Green Hag, which is CR 3, would deal 1d4 damage with vicious mockery.

edited Nov 11 '21 at 20:11

V2Blast

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answered Nov 10 '21 at 22:13

Thomas Markov

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I find this interesting... Why CR and not hit dice? Alas, I don't think there's a factual answer to that. – WakiNadiVellir Nov 11 '21 at 14:49
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@WakiNadiVellir The size of hit dice is tied to the size of a creature. So different sized creatures with similar hit points pools will have a wildly different number of hit dice. So it makes more sense for cantrip damage to be tied to the expected challenge of a creature than how big it is. – Thomas Markov Nov 11 '21 at 14:52
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@WakiNadiVellir there is also basically no consistency of number of hit dice within a given challenge rating. – Thomas Markov Nov 11 '21 at 14:55
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Note that proficiency bonus on monsters is also tied to their CR, not their HD - monsters have a +2 if their CR is less than 5, +3 from 5 to less than 9, etc. In general, the system treats CR as a proxy for character level for NPCs. – Xanthir Nov 11 '21 at 19:07
@WakiNadiVellir: Are you are coming from a 3E background, where attack bonus and other factors were tied to Hit Dice, by any chance?...this is no longer the case in 5E. – sharur Nov 12 '21 at 18:04
Well, I'd expect a bard with 8d8+8 hit points to do 2d4 damage with Vicious Mockery, is all. This once again demonstrates how NPCs and PCs are different things, with different rules. – WakiNadiVellir Nov 13 '21 at 16:55

score 27 · Answer 2 · edited Nov 17 '21 at 18:05

Use the Green Hag's challenge rating as though it were her level

According to the rules on innate spellcasting (MM, p. 10):

If a monster has a cantrip where its level matters and no level is given, use the monster's challenge rating.

Thus, a typical Green Hag (MM, p. 177) would do 1d4 damage with Vicious Mockery, because her challenge rating is 3. However, a Green Hag that is part of a coven would have a challenge rating of 5 (ibid), so it would do 2d4 damage with Vicious Mockery (as though the spell were cast by a 5th level character).

How is cantrip damage determined when cast by NPCs?

2 Answers2

Use Challenge Rating.

Use the Green Hag's challenge rating as though it were her level