Wtf. How can you find this hard? Just be an assassin, and kill every creature that comes. Click on them then press 'a', then 'e'. I got to lvl 106 with the whole map filled with the power towers all upgraded. Quited only coz it was laggy and boring. 2/5 coz too freaking easy. A baby could do it, literally.
 "Remnants of Skystone"){kind=icon}
 "Feel the Beat (F2Jam)"){kind=icon}
 "Duels Defense"){kind=icon}