For the hard badge, max your loot and magnet (i.e. the 3rd and 4th upgrade of looting) at the beginning to get more money; then increase your speed. Make your self as weak as possible, dont upgrade your attack or fire rate. Use the increased speed to dodge enemies' attack, try to hit the enemies with higher hp (e.g. the blue shark and the small boat), in this way you are harder to kill enemies and your "boss arrival" bar fills slower, this means you have more time to see the treasure box, more treasure box = more money = more score. In conclusion: avoid killing enemies and always hit treasure box. Only upgrade your attack if you think there are too much enemies and bullets that you cant handle them anymore. Later sell the 3rd upgrade of looting to buy other upgrades. My final upgrades were 4th weapon, 4th fire rate, no speed upgrade, 4th looting, 3rd and 4th flags. I earned the hard badge in this way, hope it helps :)
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