If your having a problem with a level, the best solution is to go back and redo a level you found simple for easy money to upgrade your soldiers. Right now I have a nice little set up that allows me to pick any level on normal and get the bonus money from it (mind you level one on normal you get 1000, level 2 2000, etc) do the same thing on hard and epic as well until you have your troops leveled up enough to handle it.
And for set up it dosn't matter much of what you pick I guess if you don't mind losing a lot.. but definately level up the pixie unit and use them in your battles, needing that extra health booost but not enough mana? these pixies will rock your world then ;P
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