I do like the Rewards, but I think there should be some more creative ones, like
"Knock an enemy into 3 mines in one turn",
"Have an enemy completely circle a planet, then burn in a sun", or
"Kill 2 enemies from the blast of a dying enemy"
I suggest adding a variable called something like "isaBoss" and have the boss or miniboss come out only when it is 0, and change it to 1 when they spawn. This keeps 3 or 4 bosses from being on the screen at once. You will also need to change the explode function on the boss and miniboss script to set "isaBoss" back to 0 when they explode.
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