I just don't like set angle toward player in side scrolling platformers because it targets the origin image point and starts rotating the object toward that image point. I prefer to set a defined angle for the boss then move it forwards at that angle. I am using the boss move forward a number of pixels action, it will move at the current set angle so usually 180 or 0 (left/right). Instead of this move forward however, you can use platform behaviour to simulate left,right presses which also works, either of those two options will be fine. I can send you a capx example if you want but it is just 3 events and you're already using 2 of them!