It really seems like you can't advance unless you buy the upgrades. I found it extremely hard to get anywhere unless you bought stuff and the game was really slow and when it did take off I had already finished the game. Wish there was a "huge gun" upgrade that was crazy expensive just so i could kill everything with easy.
This game is so great, so many aspects of the game. Try past daily challenges and some force you to use monkeys you would never use unless your bored because you know super monkey dominates everything. Then be forced to use the unit specials. (Spikes coves the whole track is spikes). New maps and even the reverse mode. How Epic is Bloons. By far my Favorite TD game of all time.
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because your not using SWERVE (spacebar)