for all the people having trouble with lvl 3: a headshot with a shotgun instantly kills a giant zombie. that way you can clear the groups of giant zombies pretty quickly.
If you play through the game, you will find scrolls, which you can use to teleport to the shop. There you can sell equipment that you found to get gold.
@LordBucket Yes indeed, juggling is a huge part of this game. And just that part is what makes it unique. Other TD's require you to build, and then wait while the monsters walk through your maze and you just need a good tower setup. In bubble tanks tower defense, you need to have skill to complete the harder levels.
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