One of the Divine Items, Tiamat's Brain grants the user a form of Item Magic known as Mind Magic.
Mind Magic allows the user to manipulate the brains of the target in many ways. One is through illusions, which it can cause the target brains to see. These illusions can be harmful or, tied into the next thing Mind Magic can do, can cause harm.
Because Mind Magic can make the brain believe something is happening. Most notably, it can make the brain believe the body is taking damage, thusly making the brain injure the body by tricking it into thinking the body has already been damaged. This ability has been called False Harm, and has been utilized in different ways, be it auditory, visually, or even through dreams/nightmares. It is limited not by what the magic itself can do, but by what the user can imagine themselves doing to the target. The final thing Mind Magic can do is controlling the minds of its targets. It can only control three targets at once, and those targets roll wisdom saves to resist when the spell is first cast as well as each turn after to break free of the control. Once a target is controlled once in a battle, they cannot be controlled again.