Well, the thing is......
I just can't seem to beat the Avatar or the Warboss. I want to do it badly, but I can't vanquish either of the two! Perhaps you could give me some advice?

this is what I did but I was kinda lucky I had the things in the first place.

Any way I went in and got him down to around 3/4 health then retreated my guys out of the area. Then I used orbital bombardment *twice* and it killed the warboss and almost finished off the avatar as the avatar summoned all its buddies i then used artillery stroke on it and it died. This requires you to have the commander able to use the bombartment twice which is one of his most advanced skills.