I rarely comment on games, but I agree with satorian that the pause issue needs to be addressed. I was very happy with the score I had achieved, but found myself frozen after pausing the game.
On a lighter note, I really enjoy the game and can't wait for more content!
Though it's not an original concept, but fun as hell. A few minor things I would've liked to see: A 100% Difficulty boss. If you're going to do a "%" as a representation of difficulty, why not have a 100% hardest boss? I also felt that the health minions were a little overpowered, maybe do a maximum to the number of each type you can use?
No misses for the first 3 days:
Just buy all the "Fire" cannons you can and don't attack AT ALL. Just avoid. I bought 2 Ground and 1 air.
It actually gives you the achievement at the START of day 3, it's actually pretty easy.
Edit on my previous post:
I would suggest moving the 2 minutes in Wind to Level 7, it's much harder than any of the Level 7 achievements and there's already a Wind Task in Level 6 (Kill 200 enemies)
The hard badge should seriously be an impossible. I've had almost every mini game near 4.0 and they all get virtually impossible from 4.0-5.0, some are impossible before then.
 "Endless Migration 2 DEMO"){kind=icon}
 "Nuclear Outrun"){kind=icon}
 "Fixation"){kind=icon}
 "Super Villainy"){kind=icon}
 "Burrito Bison Revenge"){kind=icon}
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 "Icy Fishes"){kind=icon}
 "Greedy Ghouls"){kind=icon}
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 "Orbical"){kind=icon}
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Glad you enjoyed it! :)