Okay, I made my comment. :) It's a little long-winded, but I hope you find it helpful. :)
...Probably some novel approach to Revenants and Mancubi.
Oh yeah, I forgot to address this. The best approach is to not let them shoot you. :D That probably sounds like a joke, but it's true. Use cover and corner-shooting or radar-shooting with the shotgun whenever possible, because their rockets hurt! :|
More specifically, though, it's worth noting that Revenants are bullet-resistant, so the shotgun is a much better choice for dealing with them.
Also, you were questioning (in the video) how Mancubi work... They have unusual AI in this version of DRL; they fire a burst of three rockets as soon as they see you, and then, a few seconds later, they fire a second burst of three rockets in your direction whether they can see you or not. (Unless you interrupt the second burst by shooting them) So if you are unfortunate enough to get shot at by them, take cover, because a second barrage is coming!