The mental coach positively influences the form of
your players. The higher the efficiency of the
mental coach, the higher your players form will
usually be.
The mental coach also affects the team's spirit positively. The team spirit always has a specific target value it slowly converges to; the better the mental coach, the higher that target value will be. A good mental coach also increases the speed with which the spirit rises towards a higher target value, and respectively slows it down if it is is decreasing toward a lower target value.
You need a medical centre to hire a mental coach.