Adjudicating Conflicting Spells

[Inscrutable]

Last night I ran a session where I ran into something confusing to me. I would like your input on possible ways to rule.

In battle I played a Lamia who cast Mirror Image on herself, which, according to the description, creates three illusory duplicates of herself. Now, I have two druid characters who love to use Moonbeam, an annoyingly potent spell. They had wiped out the rest of the enemies with Moonbeam and then moved it onto the Lamia. Now, what should happen?

According to my understanding, Moonbeam is an AOE. You roll a CON save whenever you start your turn in it or enter it. But how does that interact with illusory duplicates? Mirror Image says they are only destroyed when an attack hits them. They don't have CON saves and the description also says they ignore all other damage or effects. So.... Does that mean the real Lamia also ignores them? Does it make her immune to Moonbeam? Or is it totally ineffective against Moonbeam and Moonbeam just goes straight at the Lamia, ignoring the duplicates?

I ruled the last way, but I am doubting my logic and want to convince myself for if/when it happens again.

[JackPhoenix]

Anything that doesn't involve attack roll completely ignore Mirror Image. There's no conflict.

[Man_Over_Game]

Mirror Image redirects ATTACKS from the character to the images. Moonbeam is not an ATTACK, so it just hurts the player as normal. Since the Mirror Images aren't being attacked, they are not affected, assuming Moonbeam has no special interactions with Illusions.

[Unoriginal]

Anything that doesn't involve attack roll completely ignore Mirror Image. There's no conflict.

This, indeed.

[Inscrutable]

Okay, that makes sense. Little underwhelming defensively then.

[No brains]

Okay, that makes sense. Little underwhelming defensively then.

Some things have very powerful melee attacks, potentially with additional effects. Getting the chance to no-sale three of them is aptly whelming.

[sophontteks]

Wouldn't call it underwhelming. Its no concentration and can soak up multiple attacks.

[Deox]

Okay, that makes sense. Little underwhelming defensively then.

Mirror Image just fulfills a different role. More caster-y types may favor Mirror Image as it does not require concentration and may be a bit more versatile.

[Man_Over_Game]

Okay, that makes sense. Little underwhelming defensively then.

On the contrary, Mirror Image dramatically increases your effective AC, requires no concentration, and the benefits cannot be easily removed.

Consider something like Blur or Aid. If I had the option to take Mirror Image, I'd do it in a heartbeat.

And, in the benefit of Mirror Image, it IS an illusion. To say that they can absorb an AoE is ludicrous when considering the narrative, and for the game to not damage them despite being blasted with an AoE is lucky.

[Inscrutable]

On the contrary, Mirror Image dramatically increases your effective AC, requires no concentration, and the benefits cannot be easily removed.

Consider something like Blur or Aid. If I had the option to take Mirror Image, I'd do it in a heartbeat.

And, in the benefit of Mirror Image, it IS an illusion. To say that they can absorb an AoE is ludicrous when considering the narrative, and for the game to not damage them despite being blasted with an AoE is lucky.

I guess when taken in perspective, it is nice. My players primarily play casters who use AoE extensively, so it seems worse. Only one melee player.

On a similar note that came up in the same combat, should two Moonbeams stack? Reading the rules, my answer seems to be yes, but it doesn't seem to flow super well. Is the moon extra "mooney"?

[Man_Over_Game]

I guess when taken in perspective, it is nice. My players primarily play casters who use AoE extensively, so it seems worse. Only one melee player.

On a similar note that came up in the same combat, should two Moonbeams stack? Reading the rules, my answer seems to be yes, but it doesn't seem to flow super well. Is the moon extra "mooney"?

Found the information I was looking for:
The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect — such as the highest bonus — from those castings applies while their durations overlap.

I'd consider the area of Moonbeam to be "the effects of the [...] spell". So, no, they don't stack. They both can exist in the same spot, and if one had a higher level than the other, it'd take precedence, but both spells continue to run their durations.

[Inscrutable]

Found the information I was looking for:

I'd consider the area of Moonbeam to be "the effects of the [...] spell". So, no, they don't stack. They both can exist in the same spot, and if one had a higher level than the other, it'd take precedence, but both spells continue to run their durations.
Oh, where is that? In the PHB? And would different casters doing the same spell matter?

[Deox]

Oh, where is that? In the PHB? And would different casters doing the same spell matter?

PHB - Chapter 9 or 10, "Combining Magical Effects"

Additionally, I believe there was some errata (or tweet, or something posted) that further clarified the DMG.

EDIT: Found it -

Chapter 8

Combining Game Effects (p. 252). This is a new subsection at the end of the “Combat” section: “Different game features can affect a target at the same time. But when two or more game features have the same name, only the effects of one of them—the most potent one—apply while the durations of the effects overlap. For example, if a target is ignited by a fire elemental’s Fire Form trait, the ongoing fire damage doesn’t increase if the burning target is subjected to that trait again. Game features include spells, class features, feats, racial traits, monster abilities, and magic items. See the related rule in the ‘Combining Magical Effects’ section of chapter 10 in the Player’s Handbook.”


Question on this, though. Suppose two clerics with Spirit Guardians (one with Radiant, the other with Necrotic). Different damage effects, same movement penalty.
Yes - I'd let this fly
No - Can't stack

To expand: Barbarian has been hit with Hex, targeting his STR, from Warlock A. Barbarian is hit again with separate Hex, targeting his DEX. Strict RAW would imply only the stronger of the two would "stick", though seems odd.

[Inscrutable]

Thank you, I found it, though it is on pg. 206 of my PHB. Very helpful.