The problem is the game is all fun and stuff until you reach level 20. And you literally spend as much time on the rest of the game as you do on this single last level. The upgrade system becomes stupid and you spend 30 secs after each run for not even a complete point that won't help. I also noticed that the enemies are randomized on the last level which makes it more or less easier depending on whether there are ranged or not in the 4 people groups. I first rated this game 5 stars because it was better than the first one, then 4 because it took a while to do the levels again to get the complete sets, then 3 just thanks to level 20. You need to rework the upgrade system and the difficulty scaling.
I liked this game, I like your humor and the way you think, I really identified myself in some situations. The drug part shocked me with it's precision and obvious knowledge, I can only applaude such detail and you have obviously had your part of doing drugs ;)
Here is a strategy that works for every level from level 13-14. Get 3 Giants Nightmares fully upgraded and the rest in grunts fully upgraded. Send all your grunts first, try to dispatch them inside the enemy army, but try to kill one side. Then, send your nightmares and collect every nuke you see. When your nightmares die, use your nukes to kill the remaining buildings, and remember to collect the spawning ones. It makes the game very easy. Good luck.
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xD This made me smile :)