Best reward is the camera to fix memory leaks. For Paris skulls, I used all purple parts except I used the robot's treads, arms and antenna. Go back and forth at the beginning while using the eye power to kill all humans on screen until the spawns die down, then proceed to the right and you should reach gold by the time you get there. Use the antenna to take down aircraft and tanks while you're getting skulls.
Yes, helicopters, cars and civilians make the game less fun, but if you use the spacebar handbrake you can turn as fast as you want no matter how beat up you are. Also, at the beginning if you want to grind to upgrade, simply let zombies hop on and shoot them and then die and repeat. Shooting gives far more RP than anything else you can do--don't even bother doing anything else if you're just trying to get more RP.
Too many glitches. You can't build a mega tower with more than one charge tower or the game will crash or the bullets will fly in circles and do no damage. Also I wasted time playing normally until I realized you can beat any insane level in 30 seconds by rushing all waves immediately and buy an area and ghost area tower plus range and speed boosters
It's a trap! You can trap enemies to a stop as long as there's a path from start to finish. You can even open the path after you trap them and they'll still stand there forever. Just make sure you have a powerful tower near them or you could wait forever for your weak towers to kill them
With only trolls you can grind out a win on any level. Send them in one line to draw the computer to mainly use that line and then go nuts when you get a troll charge
Hard badge isn't too bad if you're willing to spend tons of time to constantly save, see what happens the next day, reload and change your actions accordingly.
Walkthrough: Buy floors as soon as they are available, and buy turrets until you can afford a laser cannon. That's it. A single level 1 laser can murder any wave by itself. I beat the game with $335,000 left.
Glitch: get overkill and the laser and you can get 10k XP per SHOT and 100k per level easily. Something's wrong with the math because it only does 100 damage so you shouldn't get much more than 100 per kill with overkill, but some single kills give 1000+ XP.
Super money hack: Get cycle bonus upgrade for computers, use only lights to get rid of scientists to hack all the computers and save up cycles, then use up all cycles by clicking on phones and turning off lights. You'll get at least $4,000 per level.
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