I've got a gallery with a few Health Bar projects and tutorials in it, maybe you can find what you are looking for here:
http://scratch.mit.edu/galleries/view/71750
Hope that helps!
PS: This post might get more views over in All About Scratch...that's where general questions about Scratch typically get posted. I'll move it over there for you.
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In addition to what Paddle2See said, maybe you'll find this project by Tutorial_Maker helpful.
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Forever
If TOUCHING spriteGreenOrb
change INCREMENT by -1
?
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