Hello, I did some tests and came to the conclusion that the fastest way to make these 2 achievements is to do



If you are curious or interested how did I come to this conclusion here a few numbers:

I made 3 tests

Survival - Delta Sector
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Biohazard - Deta Sector (Mission 5)

Duration: Long / Difficulty: Easy

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Biohazard - Storm Sector (Mission 7)

Duration: Long / Difficulty: Easy

And here are the Results:

Survival - Delta Sector (it always last 3 minutes)
2x Attempts
1st - 86 kills / 3 minutes = 28,67 kills/min
2nd - 95 kills / 3 minuts = 31,67 kills/min


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Biohazard - Deta Sector (Mission 5)
1x Attempt
194 kills / 12 minutes = 16,17 kills/min (Worst place from those 3 choices)
(Forget to take a picture at the end, shame on me /facepalm)
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Biohazard - Storm Sector (Mission 7)
2x Attempt
1st - 335 Kills / 19:30 minutes = 17,18 kills/min)
2nd - 335 Kills / 18 minutes = 18,61 kills/min


Storm sector might be a little frustrating sometimes because a monster may get stuck somewhere in the level and you may need a few minutes to find him (on my first attempt it happened and I wasted 1:30 minute to find him)

Besides, the Biohazard levels have some seconds of cooldown between the waves, and the end-all those seconds multiplied by the number of waves made you wait 1 or 2 extra minutes.
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So let's say you kill 90 zombies on the Survival (And be sure you have your Vulcan T6 fully upgraded) that means you need to do it 111 times less than the amount of the zombies you killed during regular gameplay, on my case, I beat the game 2x Times (new game and new game plus and did all Survival + Biohazard challanges) at the end of it all I made naturally the "5.000 kill zombies" achievement, Now just need to grind, at least 56x times (168 minutes + Loading time) this Survival level and we are done, cheers!