Buy 2 shields in the swords section and put them on both sides, then upgrade the slow time upgrade.
The shields block EVERY PROJECTILE!!! only thing that can hurt you is the weak ass lightning.
When bullet time is activated, the battery bar still refills, and by the time bullet time is deactivated, the bar is full again, so you can go through entire lvl's without other balls even getting to open fire at you (yes, it stops then from firing)
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