This hard badge isn't too hard. Just go exp/money upgrades early, then get one of each (start with electric) turret on each side and then upgrade them. For the final level, 4 saws worked out best and 2 of everythng else is what got me through. Also, taking waves early seemed to work well, start with an advantage then maintain it with that extra money.
There's a couple of levels I lost because of luck, for instance the one with the massive snaking tunnel, my ball got physically stuck in the tunnel, but apart from that it was a pretty good game. One of the few hard badges I found enjoyably challenging.
Okay so, pretty easy hard badge imo. I just kept levelling up with 50% strength, 25% defense, 25% vitality. Every single level just stay at the edge of the map so they cant surround you and SAA attack should ensure they basically never manage to hit you. The only problem you'll have is the rage beavers which can be frustrating, just try to focus them down ASAP while avoiding attacks, then go back to the normal strategy. The final boss, same strategy, if you time the SAA attacks right he wont be able to hit you either.
The game itself was actually quite good too. The world needs more beaver games ^_^
Yay for maths? It lacks a back to menu button once you started playing, when you win it takes a bit too long for the score to be calculated, sounds get annoying. The flash seems to work though.
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It got stuck!? I tried that level SO many times and I thought it was safe from getting stuck! Sorry.