Scratch that. Same strategy (see last comment) except mix in splash towers around the outside of everything for the win. Just be super careful to not let a buff drop where you can't reach.
Put a ring of water towers around the two spawn points, but leave a few holes for enemies to leak out of the ring in a semi-controlled fashion. Keep your wizard running in circles around the outside of the ring. Leave enough room around the outside to maneuver around the few enemies who get in front of you. Put stun statues on all of your towers. Your wizard should be able to one-shot many of the bats if you max out his experience. The rest are now far too slow to catch you. Eventually a couple enemy buffs will land in unreachable locations, the monsters will become unkillable, and you will lag more and more until you die.
Wow, a point and click game that is not based in logic. Why am I trying to make a tin man? So I can put a photo next to it and get the can's contents. Of course. How else would you open a can? Or rip open a bear that already has a big hole in it? Or light up a drawer that is already located directly under a lamp? Seriously, for every problem you encounter in this game, think of the LEAST logical way to solve that problem. Anyone who claims they solved this without hints either created the game, is lying, or is just the right amount of insane.
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Keep in mind "The Wizard of Oz" and everything will seem very logical, in its own way. :)