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The boss is already available in the entities list, with the script and all, but it is not functional. I used the screen-shot provided by BMcC to set the nodes (have been very helpful), had to modify the script a bit (basically uncomment things), and it worked very nicely, wonder why they did not include it in Aquaria.
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It will be included in the mod we are currently developing, Magic of Aquaria 
WHOA, that's awesome of you! How totally unexpected.

It's great to see, even years later, that my work didn't go to waste! So, so cool.
But PLEASE don't tell me what the script looked like... *shivers*