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Nice idea, fairly well done.
The collision detection feels a bit iffy, though, and there are too many negative power ups that you get no warning about and have a high likelihood of killing you completely (e.g. the spark that burns the trampoline, the gas tank).
Level 14 is pretty irritating with all its birds. As is losing control of the trampoline thingy when you move the pointer off the screen left or right, but having it go into pause mode when you move off the screen vertically: why is either necessary, why can't I just have control all the time?
I'm also not crazy about having to replay the whole game because level 20 was missing.
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These are some *amazing(ly annoying)* birds. I think I stomped on some of them 4-5x, and they're still flying about like nothing happened.