Long topic, but yes, the oceans are inhabited by merfolk and sahuagin nations. It's touched on in the Stormreach sourcebook.

— Keith Baker (@HellcowKeith) August 26, 2017

Thank you. I’m writing a campaign that takes place in Stormhome. I was also wondering if ships needed to be registered with a government.If you're docking in a Thronehold nation. Also, "Lyrandar" would count as a government for this purpose.

— Keith Baker (@HellcowKeith) August 27, 2017

I saw you wrote the UA: Eberron. Can dragonmark spells be used with spells slots as well, or are they one use per day only?one per day only IIRC

— Mike Mearls (@mikemearls) August 8, 2017

Hi, Keith! Silly question here: is Io, the Creator of Dragon Gods, related to the Progenitor Wyrms in some way?It's covered on page 29 of Dragons of Eberron.

— Keith Baker (@HellcowKeith) July 22, 2017

The Progenitors created reality but don't directly influence it. The dragon gods govern dragons; the Sovereigns govern lesser beings.

— Keith Baker (@HellcowKeith) July 22, 2017

The dragon gods are creations – or children, if you prefer – of the Progenitors. Tiamat in particular is an Overlord – a child of Khyber.

— Keith Baker (@HellcowKeith) July 22, 2017

It's all covered in Dragons of Eberron.

— Keith Baker (@HellcowKeith) July 22, 2017

@mikemearls do you regret after 13yr the phb races/classes are all FR/grayhawk/dragonlance no #eberron baked in at core level & MM the same?

— JM (@JM13136849) July 8, 2017

No – Eberron very consciously went against the shared lore of the settings, making it hard to fit in. #wotcstaff https://t.co/ek4UotpG1g

— Mike Mearls (@mikemearls) July 9, 2017

fairenough, but that leaves eberron GM’s left telling players “”no PHB is wrong, ignore it read full ECS” very often, any hope for them?

— JM (@JM13136849) July 9, 2017

Will eventually tackle Eberron, just harder to work into core material as an example that supports the core, shared pieces of D&D #wotcstaff https://t.co/gCZIIgDnkc

— Mike Mearls (@mikemearls) July 9, 2017

On the one hand "settings are too similar and generic". On the other hand "settings are too radical and different for homebrewers to use".

— David Shepheard (@ShepheardDavid) July 10, 2017

1. Find shared ground for all settings.
2. Build unique elements from/on that.
Keeps D&D recognizable, but allows for lots of directions. https://t.co/yFE3m9dKvw

— Mike Mearls (@mikemearls) July 10, 2017

Thanks for giving us hope, Mr. Mearls. Please, sit down and have some cake we made to celebrate #Eberron13th Anniversary. pic.twitter.com/s9hvUPuosX

— Gonzalo Campoverde (@gcampoverde) July 10, 2017

is there any reason why more dragonmarks couldn’t show up on monstrous droaam type races & what do you think about it?13 is a number with Prophetic significance in Eberron: 13 planes, 13 moons, 13 dragonmarks. I'd only add a new one if another disappeared.

— Keith Baker (@HellcowKeith) July 14, 2017

If it was a plot I wanted to explore, I'd have the SAME marks appear on new races.

— Keith Baker (@HellcowKeith) July 14, 2017

So, suddenly goblins have all the traditionally human marks, gnolls have the mark of Shadows, harpies the mark of Storms, etc.

— Keith Baker (@HellcowKeith) July 14, 2017

So: the number of marks remains fixed, but they are suddenly appearing on multiple races.

— Keith Baker (@HellcowKeith) July 14, 2017

completely new 13th/4th/etc marks, but thinking more I think limiting them to aberrant marks is more interesting & fits the prejudicesofbothI have no objection to having Aberrant Marks appear on additional races. We had my Dragonborn PC gain a mark in a 4E campaign.

— Keith Baker (@HellcowKeith) July 14, 2017

So, if you do Eberron, or a number of settings, a new set of core books might be required to cover the differences from the main 5e?No, you'd just need a "core supplement" of sorts to bridge the gap between core 3 and the setting; Xanathar's for a specific setting

— Mike Mearls (@mikemearls) July 11, 2017

loved your ‘cast on espionage. #Eberron is synonymous with noir. Any advice/inspiration/resources for running? @HellcowKeithThe Big Sleep, The Maltese Falcon, Chinatown, Payback, Brick, and for more light hearted takes, The Big Lebowski and Inherent Vice ~Kristian

— Manifest Zone 💫 (@ManifestZone) July 2, 2017

Interesting characters with complex motivations. Situations where there's no one "right answer" and where doing what's morally right…

— Keith Baker (@HellcowKeith) July 2, 2017

… may have serious consequence for good people.

— Keith Baker (@HellcowKeith) July 2, 2017

Encouraging player characters to explore their own flaws – what mistakes have they made prior to the game? What regrets do they have?

— Keith Baker (@HellcowKeith) July 2, 2017

Establishing things people care about – NPCs, places – so those things can be threatened or lost.

— Keith Baker (@HellcowKeith) July 2, 2017

Well, #dnd5eIn #dnd5e there really isn’t a system for flaws, but it sounds like you are encouraging flaws in a characters backstop, which would work… does have a simple system for flaws on page 124 of the PHB – and if you really play to your flaw you can gain Inspiration.

— Keith Baker (@HellcowKeith) July 2, 2017

But it can also simply be a part of your history, even if it isn't an ONGOING flaw. What's the terrible mistake that led you to this place?

— Keith Baker (@HellcowKeith) July 2, 2017

Part of noir is that even the heroes aren't perfect… whether you're looking for redemption, driven by greed, or caught up in something.

— Keith Baker (@HellcowKeith) July 2, 2017

I can’t believe I forgot background flaws, that’s perfect. These are great questions to ask. tbh I didn’t really get into noir until.. And as I mentioned before, Neuromancer is sci-fi but certainly noir.

— Keith Baker (@HellcowKeith) July 2, 2017