Charles here can do some pretty groovy stuff with that brain of his, including but not limited to:
Reading thoughts
Implanting suggestions
Creating illusions
Bodily possession
Memory wiping
Obviously the mind reading will be the one most of interest to characters he interacts with. If Charles CAN read your character's thoughts, please use this post as a place to mention anything they might be thinking about during a conversation that you think would be relevant, or just anything it might be useful to know (you can also use brackets during threads for this, of course).
He can also read minds over a certain amount of distance, so after the first time speaking to him in person, even online conversations may not be safe.
If Charles CAN'T access your character's thoughts, I need to know that too, as it will stand out to him.
Handy list:
My character's mind CAN/CAN'T be read.
(The reason my character's mind can't be read is....)
(There are limits to what can be read and those are...)
(He might be especially likely to notice my character thinking about...)
(Please don't have him notice my character thinking about....)