Space Purge
The wrong pickup rewrites a good pattern
Free to play, no install step
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What playing this feels like
Space Purge scrolls steadily forward with enemies arriving in designed formations rather than at random, which means the order of the waves becomes learnable after a few attempts.
The thinking part is the pickups drifting through. Each rewrites the firing pattern the instant it is collected: one sprays wide but weakly, another drills straight ahead but narrow. Taking whatever floats past without considering the situation can strip away exactly the pattern that suited the formation now approaching.
Difficulty rises through the density of incoming fire. By the middle of a run there are narrow lanes to thread rather than open space to drift through. Players who survive that stretch tend to hold the middle of the screen, where an exit remains available on either side.