How come everyone is facing such difficulty with Zombogod. I beat him on my first try (no kidding, I am currently playing survival and my score is 15,231,499 and I'm still alive). Although I already had everything upgraded to max when I faced the boss. In such games you shouldn't play the next level right after you've unlocked it. Play the previous levels again and again until you've stocked enough cash for upgrades. When the upgrades become too expensive for the current levels, beat the new level and then replay again and again until you've stocked up enough money to max everything out. That's just my personal opinion on such games and generally on rpg and strategy games everywhere from arcade to console games.
 "Zombo Buster Rising"){kind=icon}