Question: Does "the first time the creature enters the area" include when it's cast?

Quote from Barlo >>

Question: Does "the first time the creature enters the area" include when it's cast?

 I don't think it does. It's worth googling sage advice on this spell for some extra clarification

Entering an area corresponds moving into it's area rather than it appearing on them. So, no. They will take damage at the start of their turn anyway though, unless something pulls them out before that.

Check out the latest Pax South AI video for how Jeremy Crawford allowed it to be used to damage an enemy right as it was cast...

What kills it for me vs. Flaming Sphere or Spirit Guardians is the requirement to use an action to move it.  Flaming Sphere (which I'll use until I get Hex and Spiritual Weapon) only requires a bonus action, and Spiritual Guardians works within 15ft of me, so uses my movement.

Quote from belfastbiker >>

What kills it for me vs. Flaming Sphere or Spirit Guardians is the requirement to use an action to move it.  Flaming Sphere (which I'll use until I get Hex and Spiritual Weapon) only requires a bonus action, and Spiritual Guardians works within 15ft of me, so uses my movement.

 Yeah but you have the added bonus of this spell to also force a Shapechanger to revert to his human form.

Wich is situational i'll concede, but can be usefull, in Curse of Strahd one of our players as contracted Lycanthropy after a run in with Werewolves, the party druid, plan to use this to revert the player from its transformation until they get their hands on a remove curse scroll or the Bard can learn it with its Magical secrets feature.

Aclaration in 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.

Another big benefit is radiant damages(Moonbeam) vs. Fire damage(flaming sphere).

Fire is one of the most resisted damages in 5e if people are using vanilla mm enemies. 

It can affect multiple creatures far outside of melee range (flaming sphere's only going to affect multiple creatures if they're immobile), and deals more damage. It's still a great spell even as an action to move. If your game has frequent opportunities to rest, or few encounters/day (admittedly this is most games, apparently?), then yeah, flaming sphere gets a lot better. 

Moonbeam
120 ft range
Affects all creatures in 5 ft cylinder at the *start* of their turns (or entering it)
2d10 (11) radiant, save for half
Action to move
Rider effect for shapechangers.

Flaming Sphere
60 ft range
Can ram a single creature, also affects creatures within 5 ft at the *end* of their turns.
2d6 (7) fire, save for half
Bonus action to move.
Can make references to Great Balls of Fire.

Spirit Guardians
No range (big radius though)
affects creatures within 15 ft of you at the *start* of their turns (or entering it)
3d8 (13.5) radiant or necrotic, save for half
No separate action to move, moves with you.
Lasts 10 minutes instead of 1.
No friendly-fire

Question: If the caster uses their action to move the beam over multiple enemies does it  damage every enemy the beam passes over, or only the one it ends its movement on?

Question: Is there an official answer on whether or not Moonbeam would effect the shapechanger ability of the Changeling player race?

Per Jeremy Crawford's Sage Advice column, moving the beam so that it passes over enemies will not damage any of them. The damage is inflicted when a creature enters the beam for the first time on their turn, or if they start their turn in the beam. In other words, even if you cast the beam directly onto an enemy or several enemies, or move the beam so that it is on them, they do not take damage until their turn, and then only if they are still in the beam by the time their turn starts. Think of it as moving a hazard around the field, and not like a laser that melts everything in its path. Of course, this is RAW, so with DM discretion you can make it super OP and act like a laser instead (e.g. creature takes damage when spell is cast, when they start their turn in it, any time it passes over them, and multiple times in the same round if they are pulled out and pushed back in).

Thank you!

Quote from Chaosrex >>

Wich is situational i'll concede, but can be usefull, in Curse of Strahd one of our players as contracted Lycanthropy after a run in with Werewolves, the party druid, plan to use this to revert the player from its transformation until they get their hands on a remove curse scroll or the Bard can learn it with its Magical secrets feature.

While this is perfectly in-line with RAW, it makes me chuckle to imagine a beam of pure moonlight improving a lycanthrope's condition rather than aggravating it 😝

Yeah its funny in its own way.

Quote from Ozmer82 >>

Question: Is there an official answer on whether or not Moonbeam would effect the shapechanger ability of the Changeling player race?

 IIRC Changeling are Humanoids types that can shapeshift.

The spell is most likely refering to creatures that have the Humanoid (Shapechanger) type.

Changeling while having the Shapechanger ability, doesn't have the Humanoid(Shapechanger) type, they're just humanoid type.

But thats just my reading of it.

Jeremy Crawford has said that Moonbeam does not deal damage on casting

I have found both using this and watching another player use this spell that it is a great spell... until you reach level 5 and your cantrips that do damage do about the same damage and you gain other spells that do better AoE effects.

I would not say it is overpowered or underpowered, it is just adequately-powered for the level you gain it and the levels you can't use anything more powerful than this spell, but once you get access to some better stuff it tends to be kind of a waste of a spell slot unless you are fighting a lot of creatures that clump together in very tight spaces or shapeshifters a lot of the time.

Good spell for what it is, but gets passed by as you gain power.

Given that it scales with a d10 per slot level over second, this does excellent damage over time. 2 rounds at druid level 5 will do 3d10 per round. That's about 16.5 damage on a failed save, or half on a success; this number goes up by 5.5 for every slot level, capping at 49.5 using a ninth level slot, per round! Radiant damage type is great, too.

Using an action to move it doesn't hurt a land druids all that much, as it leaves their bonus action available to cast healing word. Flaming sphere uses the bonus action, so a light cleric will need to get close to cast cure wounds.

Circle of the moon depends heavily on their forms' Multiattack, and they'd likely have disadvantage on the save if they get pushed into the beam themselves and risk reverting to caster form in a dangerous place unless they drop concentration. For them, I wouldn't recommend this option.

Does anyone else find the area of effect weird? It says under range that it's a cylinder 5 feet across, but in the description it says it has a radius of 5 feet, making for a diameter 10 feet across.