Hey! I've kinda been working on how Kassy's illusions function. If you want to know the details, let me know. I try to keep her power something that can't be easily abused or overpowered. I also try to leave the player as much control over their character as possible.
For example, someone who's studied mind control and how to resist it, or has similar mental powers themselves is going to be MUCH harder to fool. On the contrary, someone who doesn't have any experience, or is just kinda... shallow, probably will be easy pickings.
There's also things like someone being able to notice something wrong with the illusion itself. Kassy's pretending to be Reece, but a couple details probably aren't going to fit if the others know him well enough. Like... Kassy didn't know his eye color at all, so she just went with brown because she knows that's common for humans. She's got the goggles down to attempt to cover it.
Now, if someone else knows that Reece's eyes are actually a lovely blue, and they see that this "Reece" is not, then things get weird. The illusion will start to look more and more unreal to them specifically, and once they break it, it's hard for Kassy to fool the same person the same way.
*shrug* I'm trying to make mind control something that isn't an immediate godmodding trip. I think it can have plenty of leeway to be just another ability, but even I have to temper it. I mean, Kassy could break Manny's brain and make him think he's a little girl, but it will NOT be easy - or even permanent.