I have decided on Bite, Piggy, Med Pump to start, first back Explode + Bite Damage/life upgrades, then one point of Slowdown during explode, then both explode recoil reductions. Explode is really scary when you can use it and not ever have to worry about dying with it. I've gotten so many sneaky kills that I would've died with if I didn't have the recoil reduction. Then Max HP, gun upgrades, etc.
Also if you have a Voltar leveling heals then you're basically unstoppable, push every turret, dgaf
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