Here's something I did recently.
<img src="http://s11.postimage.org/ipufah8ur/Untitled_1.png" border="0" />
Someone better than me at C2 can probably provide a better way of doing this, but here's an explanation of what I did. As you can see, I created a trigger (a colorless, invisible sprite) that at once deactivated the cam and did two other things, one of them activating the boss. The boss was placed on the outside of the layout, and the instructions in the "Boss Setup" reflect this: I set its speed, had it move left (I used platform behavior for it, you might not), had it wait X time then resumed its movement ("movement" in my case is different, since I cannot give it preset pathfinding based on simulated control alone, so I deactivated simulated control and set it to move along an horizontal Sine wave - he's at sea so the wave behavior is a plus).