Early in the game I was battling some Mindfraggers and I knew what they could do so I attacked the head to disable it. Well, one of them controlled one of my soldiers and low and behold I could NOT remove it because it was already at zero hit points. That’s a restart.
The solution to the those damned things is simple: bladed helmets.
Sirens also mind control where they’re heads are disabled. .
For the Mindfragger it’s a bug I guess. They shouldn’t be able to attack you without a head in the first place.
To mind-control, a Siren must have at least the same will power as the target.
When you remove its head, you take away 30 max WP which is usually all that it has. Some Sirens do have more than 30 WP near the end game.
With 0 WP, a Siren can still mind-control your soldier if he/she has 0 WP. It won’t be able to keep control though since it costs 2WP each turn. So you’ll get your soldier back before anything happens.