Hmm i get what you are going at, i really should try higher difficulty's. Weird thing is i have tried a lot of towers on normal, and followed some insane run builds. And never got over 130 frog kills. The 510 lifes going into the boss rounds just really helped. all to 3/4 of frogs died on first round. the rest on the second.
http://steamcommunity.com/id/rollow/screenshot/307738934721245649
http://steamcommunity.com/id/rollow/screenshot/307738934721314091