In response: First endless mode, around 350,000 earned EXP it became unbearable. It seemed to me that somehow, missed enemies keep cluttering the buffer or something, because I missed a lot of enemies along the way. Slowdown occurred only with enemies on screen, and did not persist through dying.
Endless mode can't be beaten because there are too many slowdowns in the later levels. By the pattern of that slowdown, I suspect that there's a memory leak somewhere. Please check on that.
I haven't experienced any slowdowns, but it sounds bad. Could you be more specific? Which endless mode did you play? What was the pattern that makes you think it is a memory leak? At what point did it slow down? Did the slowdown persist after dying and restarting? Did it persist after restarting the game? The more details you can give me, the better.
I don't want to get rid of them, just make getting them less important, which I think the latest update did, though it may still need some more testing. =)
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There kind of is an upgrade for that: Salvaging. With enough of that you will hardly ever go without spread fire. =)