I was halfway sure that you took the initial inspiration from it. it's even better if you didn't :)
there ain't much to check out, really. EtG is a bullet-hell hell game, and there's an item called Turtle Problem. what it does is spawning little turtles that can absorb a couple of shots before ceasing to exist. they don't shoot, just cover you randomly. it's only just a few of them at first but if you play long enough you'll see, like, 20 to 30. partially reminds me of your idea but that's pretty much it. although EtG is a very creative game, you may find inspiration in some of its many other mechanics