Got to level 37 on casual at Furry Robotics. Didn't lose any hearts either.
My Strategy is to only use a pistol for a while.. then get the uzi at like wave 6 or 7 its hard but you gotta really go for headshots, and save up enough to open the two doors and get the Psycho. then you can save ammo and use the pistol again sometimes. save up for a big gun. i saved up for the LE..
I didnt unlock jenny either. ill do that next time. anyone ever get passed wave 36 on furry robotics? i was kinda wondering if i set a record. but it was only on casual