Include one control hero (or boost hero) in each lineup that you don't have leveled up. The following Heroes can be quite weak and still be included in your lineup to cause some trickiness for the defender and lower the power of your lineup to maybe push you out of the gold:
-Krak or witch for speed control
-Enchanter for tricky energy drain mid battle
-Catapult, Dust, assassin, aqua for damage boost (their boost continues even after they die...eg assassin might die immediately but pair with archer or other piercing hero and they can still be devastated by the piercing bonus)
-faith for his physical resist boost or one of the magic resist heroes like stepladder, sven, backpacker dude or Velma potter
You might even try to include both Crimson witch and krak in the same lineup to really drop the power but still make it difficult for your opponent.