OK THIS IS HOW TO DO 300 CHALLENGE!! I suck so I failed a lot until I did it this way. Buy a grenade gun and max out all stats. Then buy as many repairmen as you can. Then buy a quake box. I think I upgraded the quake box's fire rate twice and then realized I had no wall, so I think I had enough money left to buy one wall upgrade, not that I needed it. Just keep pumping grenade rounds into the front row of their advance. Between the grenades and the quake box they are on the ground more often than not. And the few who do get to the wall, whatever damage they do is canceled out by the repairmen. I finished at 200/200 for my house. Good luck and keep this alive for everyone else who sucks as much as I do at this game.
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