I finished the game with Setas on instead of power boosters to get the impossible badge, but everything else close enough to the same. Seta + Absorber means you can slow your way through the hardest parts of anything, and you can rapid toggle the slowdown to get a lot of scrapes and pick up absorption boosts along the way. It has good sustain and I found the combination to be a godsend against the 5-6 boss. It's significantly harder than the rest of the game.
One general advice on the 5-6 boss: In his final third, he starts summoning bombs. You have to get to the bottom middle as quickly as possible, as you'll get trapped almost anywhere else. Immediately after the bombs, get away from the bottom middle, because shortly after this, he'll summon red orbs from offscreen, which will instantly kill you upon spawning if you stay there. Both these phases killed me the first time I encountered them due to the sheer cheapness of them.
Something I've noticed: I've found that when the game loads, and I cannot load the "achievement" section, the game will fail to record a score if I play a round. If, when I load the game, I can open the achievement section, the result of the round I play will function properly. Something to look out for if your score keeps failing to register.
Impossible badge is certainly doable, just excruciatingly repetitive until you get that perfect shot or two that gets you a good time for a map. You'll eventually get it if you plug away at it. Some maps may take several hundred tries but it'll come so long as you're patient.
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