Geez. After trying on my own for the hard badge and failing over and over again I turned to walkthroughs on Youtube.... where I still failed again and again anyway because for some reason doing exactly the same things they didn't work. The strategy that finally worked was the video by GewaltOnslaught. Worked perfectly.
For the Hard badge, I went with Ainlay's strategy. Kept investing in the energy infuser until level 10. Defeating the lvl 10 boss gave 5 bonus points. Bought the anti matter shield and after winning one more point, the heatseeker missiles. Each additional bonus point went into Investment until it was at 20% interest. Kept the spending to a minimum and by level 40 I had 1,350,000. Maxed out what I could and kept buying hp / shield when cash was above 1 million. I didn't buy the sticky shield. Found it was a distraction and in the latter levels, you simply don't have time to aim and shoot.
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