Mindbending is a simplified term for a broad range of psychic abilities practised by Adepts of The Burning Sodality, and encompasses such things as projecting illusions, inducing states of pair, fear or euphoria, or even imposing ones' will on others. Practised in a group it can be very powerful, scaling to the point of affecting hundreds, tor even thousands-- maybe more depending on how many wielders are involved.
Mindbending beyond very simple illusions can fail against the very simple-minded, the blindly enraged, other psychics or geniuses. Its effectiveness also heavily relies on maintaining concentration and will-- if those are broken, the attack will falter. It also takes a heavy toll on the brain of the user-- pushed too hard overuse of the technique can burn someone's brain to ashes.