How do I clean the black ick off a faux copper kinetic yard sculpture?

Try soap and water and a wrap or a soft brush in a small spot first

Or buy another put in the box and keep new one and return old one

Have you tried metal or copper cleaner? Is it covered or has the finish worn off and it is down to the metal? A homemade cleaner for copper is ketchup and salt. You say it is faux copper, was it painted a copper color? You could also try the Magic Eraser. Try whatever in a small spot first.

Seems like oxidation to me. Try slathering some ketchup on a small area and see if it works. Leave it on for about 30 minutes. Rinse well. If that doesn't work than repainting with metal paint would be the final solution.

I'm thinking the original finish is gone. Take this opportunity to turn this ornament into something unique! Try a few solvents on some small spots to see what takes the gunk off - then use that to bring the piece back to the base metal. Next, check out some outdoor regular or metallic spray paints (they come in colors, too!) and find something that appeals to you. Follow the instructions and spray several light, even coats. Follow that with a clear UV resistant coating. Make sure the mechanism is in working order - clean that up and give it a shot of WD-40 to lubricate it. You're wind-spinner will be good as new!

Is it oxidation or is it sap from the trees. If it is sap hot soapy water will take it off with a little scrubbing. If it's oxidation try some rubbing ketchup on a small spot.

Try a mix of Salt and vinegar to see if works

Here's a tutorial that might help - https://chascrazycreations.com/copper-cleaning-hacks/