Try Medium level rock solids, put out one archer and level it to 8, then do the same again, then put out a wind tower and upgrade it to a level 6 doom tower, then put out an archer an upgrade it to level 4 corrosion tower, then put out a wind tower and take it to level 6, then stick out another wind tower and upgrade it to a level 6 doom tower, then another archer tower upgraded to a level 4 corrosion tower, then another level 6 wind tower, near the end put down 2 wind towers and upgrade them to level 2 ice towers voila...