This looks fantastic, a couple of questions:
1. Can a regent scheme to replace the liege with someone else? i.e., can I replace the king with another claimant/family member instead of just usurping the throne?
2. Does getting the regent in a scheme against the king outside the regency help in any way?
3. Can a regent attempt to change succession laws as well?
4. Can a regent arrange marriages and the like for the king/his immediate family? Say an underage king married to the regents daughter or an incapable rulers daughter married to the regents son. I expect that would be something that generates a lot of strife.
5. Can a vassal/vassals attempt to diplomatically coerce the regent into not abusing their power/arranging marriages/etc? The trope of an evil scheming regent usually comes along with the trope of loyal country vassals who support the king.
- Not at present, not something we'd anticipated people wanting, but you're actually not the first person to ask for it in this thread.
- Not outside the regency, though regents get a slight buff to schemes inside their liege's realm when they're in an active regency.
- They cannot - we tried to avoid having the regent literally do things for the player. It's a mire of weird UX and AI bugginess, not to mention player frustration.
Something we talked about late in development was the idea of this being something very powerful regents might try to force through via an interaction, but it was too late to do anything with. We might still do it in future.
- Per the above, you can't arrange marriages on behalf of your liege (not least because, as I guess you can imagine, the... three or so? Marriage interactions are some of the most complex in the entire title), but you do get a bonus to acceptance. It's quite small if you're just designated or in an unentrenched regency, and scales with the Scales of Power in an entrenched regency.
- Not peacefully, but you can overthrow them via scheme. If a regent is loyal, disloyal vassals are more likely to do this, and if they're disloyal, then loyal ones are.
What happens when the regent is sick? Will there be a regent for the regent?
Inception with regents? In the inner core is the real King/Queen with 50 layers of regents?
Ohhh, excellent question! There are two states: invalidation, where they're removed (e.g., you gain incapable and literally can't govern), and inactivation, where you temporarily can't do regenty stuff but retain the post. The latter is used for the regent attending small activities, gaining minor illnesses, or where we're trying to prevent easy exploits for removing powerful regents.
About that, I think it'd be nice at some point in the future to link regencies in some way to the new vassal stances, now that vassals will have favourite heirs and such - then they'd be able to take advantage of their role as regent to plot for their favourite heir to take the throne if they have enough support.

This came up once or twice.
Maybe for the future, but we were a relatively small part of the team and didn't quite have the time for something like this.
Great stuff!
Just one quick question: do regencies apply when you are out there commanding armies?
This one we discussed a lot and spent a not insignificant amount of time prototyping. Some people found it really fun, some people found it an absolute nightmare, 'bout a 50:50 split on the team, but there were also an absolute bevy of unexpected technical and performance bugs resulting from it. I think it's still something we'd like to do at some stage, but our ambitions outstripped our resources for adding it now.

Hope that covers it - long thread, easy to miss replies, so I'm not being sassy, I just don't want to type it out again.
...Landless play confirmed...??
Jokes aside, I did think about asking if landless character playability was ever on the table during the most recent development cycle, but then I forgot and this post sparked my curiosity again. So...
Player taking control of a landless character and wandering from court to court to try and be appointed as regent and then trying to coup their poor AI liege:
yay or
nay,
@Wokeg ? (or any other of you fantastic people on the dev team, of course

)
Nay, sorry to say.

That'd be a
very big increase in scope. Regents can be landless, but landless characters are still unplayable. Though uhh, much of the time, one of the first things a landless regent is gonna want to do is: acquire land.
Will it be possible as regent to somehow dictate who the
next regent will be? For example the regent's own heir. I feel like this system could be perfect for role-playing the late Merovingian dynasty / rise of the Karlings with their hereditary regency. Or depending on where you're willing drawing inspiration from even a shogun-like arrangement.
Edit: according to a quick wikipedia search this position was apparently called '
Mayor of the Palace'
Not at release, but it's certainly technically possible. I'm not super familiar with that being much of a thing during our time period (we don't generally countenance mechanics for things before 867), I'm afraid, though I could be missing spots.
This sounds amazing, though there are a few things that seemed weird or left me with questions:
Am I reading this correctly? You can only attempt to coup against a liege if they are a Head of Faith? And you can't do it if their imprisoned either?
It seems when you revoke titles from fellow vassals as a regent, you revoke them for yourself. Can you also revoke titles for your liege? For example, if you're a loyal regent, you might want to press a claim to a title that is rightfully his, and, similar to the crown authority, take the fall for that.
Ah, blast, the HoF thing is a bug. Must've taken the screenshot on the wrong branch - that's an edge case where someone found a way to coup the Papacy. Too many screenshots to manage. Don't worry, that's
not a requirement. The imprisonment thing is, though, which is partially narrative convenience (otherwise we'd need variants for all the coup types to account for if you're imprisoned, and honestly those'd sorta need different requirements, and it'd just be a whole headache) and partially to stop keeping someone in your dungeon for long enough just automatically resulting in them getting coup'd if you give it enough time.
Interesting notion - you can't at the moment, but not a bad idea. I'll jot something down.
Is a ruler imprisoned by their own vassal considered incapable, and therefore under regency?
Incapable only applies to traits (and in vanilla, only the incapable trait itself), so no. Imprisonment only causes regencies if it's foreign imprisonment - no one is going to accept that you're just being a humble servant of your liege if they're at home, just in prison and reduced to sending letters (especially if they happen to be in
your prison). Basically guarding against easy exploitation of the AI, there.