No need to max out everything, Just max out research time, weapon reload, plant grow time, then just +1 eerything else. Don't buy all the weapons, survive by buying a couple of health boosts, but make your first weapon the machine gun, then wait until you can buy the biggest weapon.
Ok, so I just finished the game and got all of the gold souls and at the very end after I finished the last screen, I found the "shop" icon where you can buy upgrades... WTF?
I would agree strongly with a sequel with campaign mode. Add some variety to the baddies, a few more upgrades with maybe a nuke option, several different campaigns with different missions to save the galaxy and all of humanity!
So, all you have to do is keep moving in one direction, I chose diagonally, up and to the right, continuously, firing behind you and I died only once before making it to the boss... You do need some points in engine to be able to go fast enough to outrun all of the orbs this way but it does make the game very fast and easy (if you are looking for that). Overall a good game but I thought it could use better upgrades and a more interesting cast of baddies. 4/5
Make the aiming arrow longer to give a better range of power... Other than that I thought the physics were good, made it through level 20 without killing myself...
500 chain not impossible, like Xenian said, don't level up and just sit still killing stuff. I got to level 5 which gave me a good rate of baddies coming in for my fire fodder, maxed out my fire rate and found some patience... It is possible Danielson!
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Once you get an airlift card, play it and select one of the 120s as the source territory.