Black dragon mask AC stacking

[Quietus]

I'm sure this has come up before, but I couldn't find anything via Google; my party has recently made their way through the Hoard of the Dragon Queen module, and obtained the Black Dragon Mask at the end. The Dragonborn sorcerer basically instantly claimed it as soon as she heard "+Cha to AC when unarmored", which is a mechanical problem. We rolled for stats, before I realized how OP that would be, and everyone rolled extremely well. So right now I have a head to head because she feels she should have her 13+dex (3)+cha (5), or 21 AC, plus shield spell. I have every intention of making her pay for using that mask, of course, since it is an artifact tied directly and intimately to Tiamat, but in the meantime, I am hesitant.

Has there been any clarification on this that I couldn't find? It feels like if she wants that bonus she should be using the base 10+dex+cha, since the whole point of Dragonborn unarmored AC is that it replaces armor. But it seems like RAW, she gets her 21 AC and becomes tankier than the party fighter.

[JackPhoenix]

As written, yes. It's a legendary item. Note that fighter in legendary armor (+3 plate) also has AC 21 (at least, before shield, spells, fighting style or other magic items).

What dragonborn unarmored AC? They don't have anything like that.

[Ventruenox]

Replace Dragonborn with Draconic Sorcerer.

[Nifft]

As written, yes. It's a legendary item. Note that fighter in legendary armor (+3 plate) also has AC 21 (at least, before shield, spells, fighting style or other magic items).

What dragonborn unarmored AC? They don't have anything like that.

The "13 + Dex" matches the dragon origin sorcerer, so I presume that's what the OP meant.

The character also being a Dragonborn would be merely incidental.

[Koren]

So abilities that determine how AC is calculated cannot combine, which initially makes me think no.

However, comparing the wording of the masks ability and Unarmored Defense (I checked both Monk and Barbarian to be thorough) I don't think it recalculates AC, I think it just adds the modifier. So, yeah, it should work.

Disclaimer; I looked online. I dunno if the wording would be any different there but just in case it is... Well, I could be wrong.

[Naanomi]

It is pretty rediculous, but it is essentially an artifact. At an AL game I saw a half-elf barbarian/swashbuckler with AC 24 or so (with a few other items)

A tortle ancients paladin perhaps?

[Lolzyking]

21 ac isn't that impressive in rise of Tiamat

So many things target saves its silly

[DarkKnightJin]

I say let them. Then have them waking up in a different place than where they went to sleep.
Have them notice a dark voice at the back of their mind, prodding them to hurt people beyond reason. To steal things from the party.

Pretty much make it clear that SOMETHING hinky is going on with this thing, and they should NOT be using it.

Look at the Artifact Detriment table in the DMG. Let her know before she attunes that there's going to be some serious drawbacks to wearing this thing.

[RedMage125]

I'm AFB at the moment, does the mask say "add CHA to AC" or "Have an AC of 10+DEX+CHA"?

Because if it's the latter, then they pick one or the other, not 13+DEX+CHA.

[Naanomi]

I'm AFB at the moment, does the mask say "add CHA to AC" or "Have an AC of 10+DEX+CHA"?

Because if it's the latter, then they pick one or the other, not 13+DEX+CHA.
Just a bonus, not a new formula.

[Sigreid]

I'd let them and I wouldn't even punish them for it. It's a cool toy. Particularly for a dragonborn daconic sorcerer, but I don't personally think it's game breaking.

If they are wearing it around town though, I think they are likely to become pretty unpopular. Especially if the local clergyman recognizes what it is. Also, one would think it would make them the priority target for any dragon cultists they come across.

[Forum Explorer]

Agreeing with the consensus here, let them use it. It is a legendary artifact. It should provide a large boost.

[Degwerks]

Let them keep it. The stats were given so it can be used by the party. If I were the sorcerer though I'd be using Disguise Self and Non detection spells constantly though.

[Easy_Lee]

No need to punish the player for something handed out by the DM. It's treasure. Let the player use it. There's no reason D&D has to be a zero sum game.

Besides, critical hits will still hit, and a single Intellect Devourer or similar could wreck the player. It's not like the player is invulnerable now.

[Quietus]

Thanks everyone - the "It's a legendary item" argument largely is what comes up in other threads I've found as well, and is a fair point. If it weren't for the fact that my PCs started with such ridiculously high stat totals, I wouldn't be so worried. It's reached the point where it's difficult to challenge them without throwing completely lethal combats at them.

I'll just let it move forward, and provide story reasons why a gold dragonborn draconic bloodline sorcerer (yes, this is exactly what's happening, sorry for screwing it up earlier) really probably shouldn't be wearing an artifact dedicated to Tiamat. Particularly since the cult will absolutely want it back.