Void Eaters + Horrors in Practice mode...well, its super hard but it can be done. You gotta figure hw to beat each of them individually in Practice mode and then when they're together, make sure you're on the otgher side of the Void Eater cannon (as in not on the same side as Horrors) or you're dead. and once you're in the proper position you can kill the Void Eater, which killed the Horror by itself. I'm now trying to get this more consistently.
VERY VERY addictive game btw. 5/5
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 "Amorphous+"){kind=icon}