How to get three stars in angry birds space world 2 level 21
Looking for another three golden stars for your collection look no further. Shoot the ice bird into the first pig as seen in the screenshot above. This will take out the pig and as a bonus it will freeze the structures around it making you more points after shooting the last bird. Now shoot the purple bird in a high arc above the structures and press down on the screen on the opposite side to make the bird change direction and take down the tower and the pigs in it. If you did it right you can decorate your phone or pad or pc with three more stars.
Looking for some more help check out the video walkthough below :
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I found an even simpler way. Shoot the first bird around the slingshot planet in the opposite direction. It will orbit and hit the structure from the back, toppling the whole thing and killing all the pigs with just one bird!