Having some fun with this new mode, this is the furthest I could get before taking damage (and presumably losing - I paused it before I did so I didn't have to redo placing the towers).
https://puu.sh/nrLGw/7eeacd46fa.jpg
Frogs had 20m~ ish health around then. I added some slow/damage amp towers and got like two waves further with 700~ kills.