RAW/RAI Teenage Mutant Ninja Tortles

I am planning to play in a goofball one shot that might turn into a longer campaign.  I’m wanting to play a Tortle named “Cowabunga” - but am unsure how one of the Tortle features works.

Specifically, they have a natural AC 17, but cannot wear armor and cannot change this with dexterity.  So I have the following questions:

1. If I dip in Monk or Barbarian to get unarmored defense, will Wisdom or Constitution add a bonus to AC even if Dex does not?

2. Will spells that add AC affect the Tortle’s AC?

3. If I played a Tortle Monk but used Strength instead of Dex, would that run into any snags later down the line I am not thinking of?  (I can read the PHB, but I’ve never played a monk before).

4. I’m not sure about the numbers, but is there a point in the Tortle Monk build where the Tortle’s claws feature is better than Martial Arts?

5. Would a Tortle still be able to concentrate on a spell like Hex or Hunter’s Mark (or any concentration spell) while in “Shell Mode”?

6. Are there any specific strange rule interactions with Tortles that might impact magic, combat, role playing, etc, that I am not mentioning here?

7. Since Tortles can hold their breath for one hour, are they basically immune to certain spells that attack the lungs/breathing?

Thanks for any and all feedback.

Quote from packman767 >>

I am planning to play in a goofball one shot that might turn into a longer campaign.  I’m wanting to play a Tortle named “Cowabunga” - but am unsure how one of the Tortle features works.

Specifically, they have a natural AC 17, but cannot wear armor and cannot change this with dexterity.  So I have the following questions:

1. If I dip in Monk or Barbarian to get unarmored defense, will Wisdom or Constitution add a bonus to AC even if Dex does not?

2. Will spells that add AC affect the Tortle’s AC?

3. If I played a Tortle Monk but used Strength instead of Dex, would that run into any snags later down the line I am not thinking of?  (I can read the PHB, but I’ve never played a monk before).

4. I’m not sure about the numbers, but is there a point in the Tortle Monk build where the Tortle’s claws feature is better than Martial Arts?

5. Would a Tortle still be able to concentrate on a spell like Hex or Hunter’s Mark (or any concentration spell) while in “Shell Mode”?

6. Are there any specific strange rule interactions with Tortles that might impact magic, combat, role playing, etc, that I am not mentioning here?

7. Since Tortles can hold their breath for one hour, are they basically immune to certain spells that attack the lungs/breathing?

Thanks for any and all feedback.

 

1.  Unarmored Defense does not say it provides a bonus to AC, so it doesn't provide a bonus to AC. It provides an alternative way to calculate your base AC, as does the Tortle's natural armor. When you have more than one way to calculate your base AC, you choose which one to use; they do not combine in any way.
2. Spells that provide a bonus to AC (like Shield of Faith) will increase your AC. Spells that provide an alternative way to calculate base AC (like Mage Armor) will not.
3. Probably not, mostly, though I don't know why you would want to do that. 
4. The Tortle's attack is an Unarmed Strike, and therefore uses the Monk's Martial Arts die, so this doesn't really matter in practice. However, it will be better than a 5e Monk's Martial Arts die until level 5. In 5.5e, the Martial Arts die starts at a d6, which is the same as the Tortle attack.
5. Yes, because nothing says it can't. As you have advantage on Constitution saves while in Shell Defense, you'll be better at holding concentration when damaged than you would be normally.
6. I don't think so.
7. Only if the spell explicitly says that. Most spells that you'd think might work that way don't.

1. You only calculate your armor once. Either with Unarmored Defense or Tortle's Natural Armor. You can't mix the two types of AC calculations. And in this case I would say Tortle's Natural Armor trumps Unarmored Defense.

2. I don't see a reason why e.g. Shield wouldn't increase a Tortle's AC. It's just a flat bonus, not a new AC calculation (unlike Mage Armor).

4. Probably not. It's the same with Tabaxi claws and other species with unique Unarmed Strike weapons. The only difference is the damage type (Bludgeoning vs. Slashing) and some creatures might be resistant or vulnerable to one or the other.

5. I don't see a reason why Shell Mode would break concentration. If you couldn't, it would say so, like Barbarian Rage. However, you can't use additional effects, like Witch Bolt, since Shell Mode says you can only use a bonus action to end Shell Mode.

7. What spells are you talking about? But in the end I think this would drop on the lap of your DM.

N.B. I've played Monk only once in a one-shot and never played a Tortle.

Differnt features can provide different BASE ARMOR CLASS plus bonuses. 

you get to pick one base AC, and only the bonuses that go with it.