How to Change the Selected Mask for the Mask of The Dragon Queen?

Question

I am playing in a 5e level 20 one shot and my DM is allowing us to choose a number of magic items. The Way of The Ascendant monk looked fun and I happen to own both the "Rise of Tiamat" and "Hoard of the Dragon Queen" campaign books so I decided to go with a heavy dragon theme.

I have chosen to have "The Mask of the Dragon Queen" as my Artifact, but I am unsure on how exactly it works. I know its listed as one of the "Problematic" items for the Adventure League as mentioned in this question, but I figure that is more for balance issues. The item description itself says

... While you are attuned to and wear this mask, you can have any of the properties from any one mask. Additionally, you gain the Damage Absorption from each of the five dragon masks, and you gain five uses of the Legendary Resistance property.

The "..any one mask." refers to the 5 dragon chromatic dragon masks that make it up, and have a lot of various buffs. All of the specifics can be found in the free PDF supplement Here but the important one to my question is Damage Absorption.

Damage Absorption. You have resistance against the mask's damage type. If you already have resistance to that damage type from another source, you instead have immunity to that damage type. If you already have immunity to that damage type from another source , whenever you are subjected to damage of that type you take none of that damage and regain a number of hit points equal to half the damage dealt of that type.

My questions are:

1. When and how can I change the mask that is 'active'?
2. Does the 'active' mask give immunity to its element since the Mask of the Dragon Queen has all the properties of each mask and the properties of the 'active' mask?

My best guess for #1 is I choose when I attune to it, but I cant find anything official. I even tried buying the item on DnD Beyond to see if they mentioned it there or had implemented it in some way. Unfortunately it doesn't look like they even tried.

For #2 I would guess not because the ability text specifies "... another source..." but figured I would check anyway.

An official ruling or Rules as Written/Intended is best, but experience with the item itself is also appreciated. Im not the type to try and min/max and am confident that my DM is ready to kill us anyway, but I'd like to avoid confusing him if possible.

Answer 1

When and how can I change the mask that is 'active'?

While you are attuned to and wear this mask, you can have any of the properties from any one mask.

You choose the 'active' mask when you attune; that is your "any one mask" for the entire rest of the time "while you are attuned to" it. You could take off the mask (losing the properties), and then put it back on (regaining them), but so long as you were still attuned to it you would have locked in your selection of which 'any one mask' you would have the properties from.

If you would like to change the 'active' mask, you will need to de-attune, and then re-attune, selecting a different mask at the time of attunement.

Does the 'active' mask give immunity to its element since the Mask of the Dragon Queen has all the properties of each mask and the properties of the 'active' mask?'

Damage Absorption. You have resistance against the mask’s damage type. If you already have resistance to that damage type from another source, you instead have immunity to that damage type.

The active mask gives you resistance to the element, and the combined mask gives you resistance to all the other damage types. You do not have immunity, because the active mask is not "another source" of resistance - it is the same source; the active mask is part of the combined mask, not a separate source or item (you know it it the same source in part because it uses the same attunement slot). However, it should be easy, at 20th level, to find 'another' source of resistance, be it a spell or magic item such as a potion.

Severin says...

Although the above are how I would rule based on reading the magic item description itself, an independent test of these rulings can be made by analyzing the Stat Block of Severin in Rise of Tiamat. Severin has a number of abilities marked with asterisks, and we are told that these are provided by the (combined) Mask of the Dragon Queen.

He has resistance to four energy types and immunity to a single one (fire).

He has an ability called Ignite Enemy which corresponds to the Dragon Fire property of the Red Mask.

No provision is made for him to switch between properties, which would be the case if he could choose from round to round, or in the moment, which mask to have active.

His immunity to fire comes because he has another source of resistance independent of the Mask; he is a high-ranked cultist. Note that all of the cultists of second rank and above (cf. dragonwing, dragonfang, and dragonsoul, but not the base cultist or the first-rank dragonclaw) have resistance to a single energy form.