Looking for possession mechanics that preserve agency

I haven't paid much attention to D&D monsters or lore for a few years, but prior to 2024 I struggled to find mechanical ways to reflect demonic possession, especially with player characters. The whole concept tends to sap agency, which harms the metagame.

The closest thing I found was a series of monsters that possess, such as the yakfolk priest's feature. But it was underwhelming, involving complete control, whereas most stories of possession in film and literature involve hosts who retain their awareness and act freely until the entity chooses to exert influence.

Has anyone encountered a possessing creature introduced after 2024 that captures this nuance? Specifically, something with these properties:

• The host remains aware of their surroundings during possession
• The entity can choose to exert control by selectively dictating individual actions without full domination
• The host gains some benefit or suffers some penalty during the possession

I'm interested because I've always liked the 3e lore of the loumara demons--a third subset of demons after the lovecraftian obyriths and the more generic tanar'ri. Loumara were essentially the D&D equivalent of possessors, described as a newer, less understood strain originating from "The Dreaming Gulf," the 230th layer of the Abyss.

If anyone knows of recent material that reflects this kind of partial-control possession, I'd appreciate hearing about it, whether it be official or third-party.

Sounds like you want some form of a dominate person spell

The spell Geas is a good base to use as a base for this kind of possession.  Geas compels players to act in a certain way, but the player retains agency to fight against the compulsion at the cost of psychic damage.  Depending on how strong the possession is, you can raise or lower the damage penalty for noncompliance or modify how many times per day the damage can trigger.

A really big draw to the game is that you have freedom for your character to take actions and influence the story. By definition, possession strips that agency away from players. They're going to chafe at those restrictions and seek to free their characters from them. A long-term possession will require players with a certain mindset which is okay with the loss of agency, so this is something to discuss with your table early on.

Quote from Stabbey_TC >>

A really big draw to the game is that you have freedom for your character to take actions and influence the story. By definition, possession strips that agency away from players. They're going to chafe at those restrictions and seek to free their characters from them. A long-term possession will require players with a certain mindset which is okay with the loss of agency, so this is something to discuss with your table early on.

Yeah, ultimately I don't think there's really going to be a good mechanical way to handle it. You need player buy-in. Treat it more liked a cursed object or the like, slip the player occasional "commands" from the entity possessing them, and let them RP it out