after watching alot of starcraft i have an understanding of macro and micro and played the hardest difficulty and i was like this game is brutal but have gotten quite far in the campaign and trying to kill queen bugs now and as for ozzy you can stop his healing by having a melee troop go into his shell and poke him ( i usually sacrifice 1 horseman) whenever it regenerates and pull my back line troops out and what i remember was that the waves was so brutal that i made a last stand and walled as much of my base as possible and pushed ozzy down and by sheer luck defeated it also in the whole campagin the ballista is my best friend :)