This will turn mc towards the mouse by a maximum of 5. This assumes the mc is drawn facing the right. If it’s facing up, just add 90 to angle.
// Find the angle towards the mouse
var angle:Number = Math.atan2(mc._parent._ymouse  mc._y, mc._parent._xmouse  mc._x) * 180 / Math.Pi;
var difference:Number = angle  mc._rotation;
// Make sure the difference is between 180 and 180 so it can be limited easily
if (difference < 180) difference += 360;
if (difference > 180) difference = 360;
// Limit the movement to 5 in either direction
difference = Math.max(5, Math.min(5, difference));
mc._rotation += difference;
