Some tips with survival (and the final boss): 1. All actions including range attacks and omnisoul take time, so poison will tick during these moves. Make sure you poison first before stunning and omnisoul! 2. Max your block, dodge, range and crit chance. All chances have a max (value becomes yellow), don't spend anymore points after you max it, unless you max all chances. 3. Try to keep your damage down by either stunning the enemy, or use magic armor. Overlapping stun and armor is a waste, try only have one at a time to maximize your protection.
The challenge of the game is to survive the beginning 10 waves, after that every level becomes a push-over. This becomes especially obvious starting from amazon levels, where your chance skills proc determines whether you can hold them off early on.
I remember this game: I haven't been able to finish it years ago because after I failed a level, out of the three buttons I mistakenly clicked the far right on instead of the middle one, taking back to main menu and I have to start over from the first mission. And today I did it again, looks like I can never finish this game @@
If you have trouble beating level 45 or 75, the key point is to wait for a lab to be fully leveled, then capture it right away with ~100 units, so that you can charge "capture" immediately. Capturing one of the two massive forts next to the forts give you the 100 units inside and will immediately turn the tides of the battle.