This game is easy. Nail gunners use them every level but the one with the guys underground.
Works easy did 5 rows of nail gunners on the last level on hard. Killed everything but they do need help form the supports.
How to beat bowl. I completed it last night.
You need to use three collectors and use them to get the two items. After you have the two items build a speed. One speed is done build a drone. Once drone is done build another drone and one more while the other is still building. Once all the drones are fully charged fire them in the ravine area were the purple stuff builds up. During them bombing build green collectors in a single line so you don't use to much energy. Once the drone return let them charge and send them out to bomb ravine then from I think you guys should be able to get it.
Why are the bosses so easy after you beat genu on 19?
Also play level 13 over and over again without the boss and you will get about 1.2mill each time.
Four Level Four you have to wait till the money on the factory gets low so every other time it skips sending out a spider. Eventually you will win. Don't loose the range units if you loose both restart.