Found this link for this cool video of all the types of assassinations you can get in Halo 4 on a new blog: http://silentcartographerblog.wordpress.com/. The Watcher one is the only one I have not yet performed.
I got a few games in with the fella that runs the site and now a new XBOX LIVE friend, SilentCarto75.
Good games Si and welcome to the Halo blogging world!