First I will show you an image to show the towers that I built for this.

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It's a bit tricky but the most upgrades should be focussed on the lower left and middle part of the defense. At the first waves I put my hero right at the spawn to kill as fast as I can to earn oxygen to keep up with the upgrades. Around the 3-4th wave you will need to have built the defense in the middle for the other route the monsters will take.

Near the end of the waves you will need to micro manage your hero to focus on killing the worms.
I had to use 2 extra life boosts unfortunately, I've not figured out how to do it without them. I'm not sure if it's possible without using them at all. But this worked at least.

Here are a few screenshots of my skills and my hero. But by now you should have most of the important skills and your hero will be fairly strong as well I expect.



- I've tried everything but it simply won't load the screenshot of my skills, but you can find them in my lvl 6 guide aswell the only change is that I also have the skill up to 75% resale value -


Good luck & please rate the guide if you found it useful :)