Can Tortles receive the non-AC benefits from magic armor?

Question

The Tortle's Natural Armor trait says:

Due to your shell and the shape of your body, you are ill-suited to wearing armor. Your shell provides ample protection, however; it gives you a base AC of 17 (your Dexterity modifier doesn't affect this number). You gain no benefit from wearing armor, but if you are using a shield, you can apply the shield's bonus as normal.

My question is whether or not this means all benefits from armor are ignored, or if it's just the AC benefits. For example, if a Tortle is wearing adamantine armor, its AC is still 17, but is it still able to be critically hit? Same goes for items like Hide of the Feral Guardian or Mizzium Armor; would you be able to use an action from the armor to cast polymorph on yourself/would you take no damage on successful Strength and Constitution saving throws?

Answer 1

You gain no benefit from wearing armor.

This seems pretty unambiguous. There are no secret rules. Gaining the benefits of magic armor requires wearing it:

Unless an armor’s description says otherwise, armor must be worn for its magic to function.

But the Tortle’s Natural Armor feature says you gain no benefit from wearing armor. So usually, the magic of the armor is explicitly going to be a benefit of wearing it, unless the armor’s description says that it doesn’t have to be worn to gain magical benefits. (I’m not aware of magic armor that doesn’t require wearing to gain its magical benefits). We will see that while this is probably the RAW ruling, it really isn’t a big deal to rule either way.

It’s easy to work with this as a DM.

There are lots of magic items. I doubt you’re running a “only magic items are armor” campaign, so it should be easy enough to make sure your Tortle player has access to usable magic items. Maybe a particularly industrious magical craftsman specializes in doing armor enchantment transfers for Tortles.

There is some rules support for just letting it work.

We also see this in the rules for Wearing and Wielding Items:

In most cases, a magic item that's meant to be worn can fit a creature regardless of size or build. Many magic garments are made to be easily adjustable, or they magically adjust themselves to the wearer. Rare exceptions exist.

It’s open to interpretation, I think, if this paragraph carved out an exception to the Tortle’s Natural Armor feature, but it definitely would not be a big deal to let the Tortle benefit from magical armor, citing this rule as support.

---

With the Release of Monsters of the Multiverse, Tortles cannot even wear armor.

Tortles were revised for the publication of Modenkainen Presents: Monsters of the Multiverse, and their Natural Armor trait now reads:

You can’t wear light, medium, or heavy armor

So under the revised version, the question is moot.

Answer 2

Not by RAW, but not everyone follows strict RAW

As Thomas Markov points out the rules as written are unambiguous, however I think this is the kind of thing that can be looked at in spirit rather than just words.

My interpretation of the rule is that a tortle can't really wear armour, since they have a fairly non-standard body shape, and because of their shell the armour won't help increase their defence anyway.

However magic armour as you say has other properties. I would suggest that thematically, if you can find armour which actually fits your tortle character there is no harm in allowing you to benefit from the additional features, and it thematically makes a bit of sense, you are draping the hide over your shell so you can call on it's powers not so you can gain additional protection.

As a DM I would see very little reason to disallow what you are looking for, but as written, you would gain no benefit at all.

Basically, that means you should speak to your DM, their style of play will decide the answer to this far more than we can here.