[HoneyBadger]

Yeah, I don't think Slave Collar works that way, does it? I was always under the impression it was curse + feeblemind + 30 morale. And that was it.

Something like a forgeable (in the sense that Lifelong Protection is forgeable) Void-based brain parasite that made you immune to mind burns, soul slays and charms, but also horror-marked you, would be fun, and thematic, and horribly, mind-numbingly creepy (always a plus!).

Maybe it would have a very small chance per turn-like the lycanthropy amulet-of giving your unit the Mindless tag (by turning your unit into a Soulless-because the parasite living off your unit's brain is, well, full.)-but once you got it, if your unit gets killed, he/she turns into a Lesser Horror (as a secondform) and attacks the nearest unit.