Bout the item dupe glitch... What it does, is no more than a few minutes of grinding and healing (for each item). I personally like that glitch cause it reduces grinding at least.
I only see 8 challenges.
In any case, finished all the missions.
For challenges, I like Robots. Hive Mind is nice, and they're pretty powerful.
Sniper bots are very nice too. I noticed the Computer doesn't use it's pre-round ability though
It ends the game early though... I prefer to play for Desert Patrol. Tougher, but better game.
In any case, trading around Qubba, you'll get a few hundred k very fast (and police will handle any robbers). The 1k tax is pretty low when you get 50k profit in a run.
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