i found a way to farm any of the normal enemies that you fight that spawn planes, don't kill them, the plane will keep dropping rubies letting you get max on all weapons if your patient
*jumps on top of car* TAKE THAT YOU DAMN BUNNIES! stupid kid you cant harm my car. WTF YOU DESTROYED IT! this is the moment i realised they could attack your car and this was about wave 26
 "Farm of Souls"){kind=icon}
 "Dungeon Developer"){kind=icon}
 "Swarm Defender"){kind=icon}
 "Bitzy Blitz"){kind=icon}
 "Rise of the Colony"){kind=icon}
 "Hands of War Tower Defense"){kind=icon}
 "Mine Blocks"){kind=icon}
 "Dude and Zombies"){kind=icon}
 "Versus Umbra"){kind=icon}
 "Doodle God"){kind=icon}
 "Bubble Tanks 2"){kind=icon}
 "Age of War"){kind=icon}
 "Arcuz - Behind the Dark"){kind=icon}
 "Momentum Missile Mayhem 3"){kind=icon}