Una script completo para usar en unity, el cual haga que el jugador apunte su rotacion en el eje Y hacia donde este ubicado el mouse

public class MousePoint : MonoBehaviour
{
    public float speed;
    private Rigidbody player;
    private Vector2 movement;
    private Vector3 mousePosition;

    void Start()
    {
        player = GetComponent<Rigidbody>();
    }

    void Update()
    {
        //Movimiento
        float inputX = Input.GetAxis("Horizontal");
        float inputY = Input.GetAxis("Vertical");
        movement = new Vector2(inputX, inputY);
        player.velocity = movement * speed;

        mousePosition = Input.mousePosition;
        mousePosition = Camera.main.ScreenToWorldPoint(mousePosition);
        float angle = Mathf.Atan2(mousePosition.y - transform.position.y, mousePosition.x - transform.position.x) * Mathf.Rad2Deg;
        transform.rotation = Quaternion.Euler(new Vector3(0, 0, angle));
    }
}