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The Moonbeam spell states:

A silvery beam of pale light shines down in a 5-foot-radius, 40-foot-high cylinder centered on a point within range. Until the spell ends, dim light fills the cylinder.

When a creature enters the spell’s area for the first time on a turn or starts its turn there, it is engulfed in ghostly flames that cause searing pain, and it must make a Constitution saving throw. It takes 2d10 radiant damage on a failed save, or half as much damage on a successful one.

A shapechanger makes its saving throw with disadvantage. If it fails, it also instantly reverts to its original form and can’t assume a different form until it leaves the spell’s light.

On each of your turns after you cast this spell, you can use an action to move the beam up to 60 feet in any direction.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d10 for each slot level above 2nd.

Last session, the party was fighting a Froghemoth and the monster swallowed up 2 party members (the Froghemoth bite action states the swallowed creatures are now in total cover). The cleric was casting moonbeam to damage the Froghemoth. I understand the you must have a clear path to target something with magic, but in that case, the spell has been cast already, and its description says the damage happens to a creature that enters or starts its turn in the spell's area. The area is already active in that case...

Should the characters inside the Froghemoth take damage as well on their turns?

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  • \$\begingroup\$ I've closed this as a duplicate, the same question has been asked before about the froghemoth, just with a different area of effect spell. \$\endgroup\$ Jan 9 at 13:50
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    \$\begingroup\$ @ThomasMarkov I think there is some finer detail here because this is an ongoing effect. Some of them continue to emanate, some do not. See here, I'm therefore not sure fireball is a good dupe, please check \$\endgroup\$ Jan 9 at 13:52
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    \$\begingroup\$ @GroodytheHobgoblin I said it was immaterial to this question. If you have a question about wall of force and entangle, you should ask it, and explain why the duplicate linked above doesn't adequately address the particular interaction. \$\endgroup\$ Jan 9 at 14:03
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    \$\begingroup\$ Linked question does not say anything about the effects of total cover on Moonbeam. \$\endgroup\$
    – fectin
    Jan 10 at 12:59

2 Answers 2

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The swallowed characters take no damage

If you are affected by a persistent Area-of-Effect spell after the casting depends on the individual spell. In the case of moonbeam, the spell states

A silvery beam of pale light shines down in a 5-foot-radius, 40-foot-high cylinder centered on a point within range.

So in this case is clear that the effect is an ongoing emanation from a point within range, at the top of the cylinder 40 feet up. The general rules for spell effects on page 204 PHB state:

A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total cover. (p. 204 PHB).

Because in the case of moonbeam, the effect continues to emanate from a point of origin, anything that is behind total cover will be excluded from the spells area, and the creatures there do not suffer its effects.

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  • \$\begingroup\$ Something of note : the light that shines down isn't defined as the source of the damage from the spell, but only as a visual effect of the spell. So the line of sight argument is correct, except it would probably emanate from the center point of the cylinder instead (the target point for the spell). Of course, that's only the RAW, and it would probably make more sense to make a ruling that the light falling from above is the source of the effect, in most scenarios. \$\endgroup\$
    – Matthieu
    Jan 9 at 13:52
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Ok, I've read the Froghemoth bite action again and it states:

A swallowed creature is blinded and restrained, has total cover against attacks and other effects outside the froghemoth.

So that pretty much answer the question in that particular case. But I would still like to know if some other cover would protect the creature entering the area, since its a overused spell by the cleric.

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