Is the Moonbeam spell amazing, or are we doing it wrong?

Question

The description of the moonbeam spell (PHB pg. 261) says:

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...

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

We read this to mean a creature takes damage from moonbeam when any of the following conditions are met:

• It begins its turn inside the moonbeam
• It enters the moonbeam on its turn
• The creature finds itself inside the beam on another character's turn, no matter how it got there

The creature will not take damage in the following instances:

• A creature moves from one part of the beam to another (obviously it had to take damage, but it won't take more damage)
• A creature is in the beam after having been inside the beam already on that turn.

Following these assumptions, our druid cast a moonbeam and did damage to two enemies, Bob and Frank. On their turn, they took damage again, killing Bob. Frank left the beam. On the druid's next turn, she moved the beam in a circular motion, not exceeding 60 total feet of movement, and in the process the beam came in contact with a dozen enemies and ended on Frank. All dozen enemies received damage, as they were inside the beam at some point during the turn. On Frank's next turn, he again took damage for the fourth time and died. On each of the druid's turns, she moved the moonbeam around like this until the fight ended (it did not exceed the time limit and she made all concentration checks).

Is this a legitimate use of moonbeam? It seems awfully powerful for a level 2 spell.

Answer 1

In a tweet from Jeremy Crawford, he says:

When a spell's description uses "enter" in relation to an AoE, the entering has to be voluntary only if the text says so.

By itself, it seems to imply that moving the Moonbeam counts as "entering".

But, in a Sage Advice article, he clarifies this:

Our design intent for such spells is this: a creature enters the area of effect when the creature passes into it. Creating the area of effect on the creature or moving it onto the creature doesn't count. If the creature is still in the area at the start of its turn, it is subjected to the area’s effect.

Entering such an area of effect needn't be voluntary, unless a spell says otherwise. You can, therefore, hurl a creature into the area with a spell like thunderwave. [...] Keep in mind, however, that a creature is subjected to such an area of effect only the first time it enters the area on a turn. You can't move a creature in and out of it to damage it over and over again on the same turn.

In summary, a spell like moonbeam affects a creature when the creature passes into the spell’s area of effect and when the creature starts its turn there. You’re essentially creating a hazard on the battlefield.

Answer 2

You're using the spell incorrectly. Note that the condition that causes the spell to damage a creature is when the creature enters the beam. It takes movement on the part of the creature (including forced movement) to do that. It does not cause damage when the beam just passes over a creature. As you note, that would be super powerful for a 2nd level spell.

As it stands, the spell is very poorly written. The meaning of "enter" in the description isn't as clear as it could be, but the spell would be way more powerful than any other 2nd level spell if it did damage just by passing over an enemy.

This reading of the rules is supported by the April 2016 Sage Advice column, which explicitly states:

Our design intent for such spells is this: a creature enters the area of effect when the creature passes into it. Creating the area of effect on the creature or moving it onto the creature doesn’t count. If the creature is still in the area at the start of its turn, it is subjected to the area’s effect.

Answer 3

It would be relevant to say, in relation to the accepted answer, that recently Jeremy Crawford has changed his official position on Moonbeam in this tweet (24 March 2016):

Regan Knight @Day_Knights

@JeremyECrawford "When a creature enters the spells area for the first time on a turn". What does this mean in relation to moonbeam?

Jeremy Crawford @JeremyECrawford

Moonbeam is meant to get you when you enter the light (not when it passes over you) or start your turn in it. #DnD

And this one (12 April 2016):

Kasey Umland @kaseyumland

@JeremyECrawford Movement of Moonbeam not count as creatures entering when spirit guardians moving into creature counts as entering?

Jeremy Crawford @JeremyECrawford

Moonbeam, spirit guardians & the like work the same way: a creature, not the spell effect, does the entering. #DnD

This has lead to him addressing the issue in the official rules answers for April 2016:

A creature enters the area of effect when the creature passes into it. Creating the area of effect on the creature or moving it onto the creature doesn’t count. If the creature is still in the area at the start of its turn, it is subjected to the area’s effect.

Entering such an area of effect needn’t be voluntary, unless a spell says otherwise. You can, therefore, hurl a creature into the area with a spell like thunderwave. We consider that clever play, not an imbalance, so hurl away! Keep in mind, however, that a creature is subjected to such an area of effect only the first time it enters the area on a turn. You can’t move a creature in and out of it to damage it over and over again on the same turn.

In summary, a spell like moonbeam affects a creature when the creature passes into the spell’s area of effect and when the creature starts its turn there. You’re essentially creating a hazard on the battlefield.

Answer 4

This is one of the most poorly written parts of the PHB, although there are plenty of others. Al's response seems to account for the ENTERS wording, which is vague and confounding. There is something being overlooked, however, in the interpretation that a creature should take damage twice during any turn to turn timeframe from the moonbeam. Notice that the description says a creature takes damage on one OR the other condition (entering or being within).

If you think about what is happening magically from the spell description, a creature should not suffer more of the searing flames damage simply because of being struck by the beam for the first time before its turn and then being inside a few seconds later at the beginning of its turn, before it has had a chance to act. The difference should be that the damage taken in the first case could not be prefaced by other creatures' actions whose turns came before that of the subject creature, whereas the damage taken in the second case could be prefaced by others' actions whose initiatives allowed them a turn occurring between the instant of the beam "settling" on its target and the start of the subject creature's turn (say from a Healing Word spell from a cleric acting after the moonbeam caster's turn and before the subject creature's turn in initiative order).

In other words, the beam damages creatures within the target 5' cylinder at the instant it strikes them, unless they have previously been inside the same beam, in which case it doesn't damage them until the start of their turn.

Answer 5

When I read the description for Moonbeam, It sounded like the target would only take damage if during its turn it starts off inside the moonbeam or walks/is moved into it. Meaning that you have to move the beam over your target and leave it there, which of course means you can't just sweep the area with it and harm everything. Now given the fact that it is a 10 foot wide circle, you could easily hit multiple targets at once with a good placement.