D&D 5E Espionage & Spies in D&D

[Lyxen]

Pathfinder’s Council of Thieves Adventurepath comes go mind

Bard are the natural Spies of DnD - Knowledge, Charisma (15+) and Skills (Deception, Performance, Persuasion) are essential and you have the backup of Dex Stealth and Spells (tech).

And I played a bard in that campaign, great experience overall and cool campaign.

 

[Rabulias]

One of my DMs had a magical quill and/or ink in his game that encoded writings and resisted comprehend languages. If you were named as a reader when it was written you could do so. Otherwise you needed to crack the code the old fashioned way.

 

[Xetheral]

Pact of the Tome. Write whatever you want in your Book of Shadows (secrets, blackmail material, agent identities, cipher keys, whatever) then burn it. It only takes an hour to resummon it whenever you need access again, and until then it literally doesn't exist and so can't be spied on or broken into.

Combine with the Linguist feat (to write it in code, giving you time to remote-destroy the Book if it is captured) and/or the Keen Mind feat (resummon your Book of Shadows only once a month to rememorize the contents).

 

[Benjamin Olson]

I think in a D&D espionage game whether or not Changlings exist and are remotely common in your setting is one of the first things you have to consider. If there is a whole race of people who as zero level NPCs can effortlessly duplicate a person indefinitely with the only way to unmask them being to kill them, then everyone in the espionage community is basically going to assume that anyone they encounter is reasonably likely to be a Changling and thus the effectiveness of all manner of disguise, magical or otherwise, is going to be pretty low. Appearing like someone just won't count for much; trust will all be about knowing the passphrases and secret handshakes.

 

[Fenris-77]

It is also reasonable that in a fantasy setting with at least somewhat-common magic, that some sort of forensic countermeasure would exist to detect Changlings. It would probably be unfair to make that super common, but as something that the rich might have it could be a great tool to ratchet up the suspense. A spell, a device, or a even a rare sort of creature would all do the trick. I wouldn't make it foolproof, the PCs deserve a chance to foil the countermeasure, but I think it would be a solid gate on an espionage game, and provide a solid reason why Changlings aren't simply stalking the halls of the wealthy and powerful taking what they like.