Credit to
Rowdy185 and
Dark Death 90 for their guides on last years version of this Challenge:
If you're going for this from scratch then I suggest playing Breakline.
Now two different characters are viable for getting a chunk of this done.
Curubani Kaur is unlocked automatically if you owned State of Decay on the Xbox 360. She starts with a special silenced weapon that does not deteriorate.
Or 'shark hoodie guy' who is unlocked by getting The Ninja achievement:
He strata with three silenced weapons.
Silenced suppressor weapons are incredibly helpful but aren't mandatory.
You can also get silent kills entering crouch mode by holding
for two seconds, then sneak up behind a zombie, hold
and press
once you're close enough. Get to one of those wide farm fields, tons of zombies and very little place to have one sneak up on you.
In order to have kills count you need to have the in-game time setting be night time. Breakdown has a random chance of starting at night when you start a new game, otherwise just play around or idle till the time changes. At the longest I had the game sitting for about fifty minutes till it switched to night. (If you just want to let the game sit by itself, either plug in the controller or press a button/wiggle a analog every once in a while otherwise it might turn off from being inactive and the game time won't progress because the controller being off pauses the game.)
Should be obvious but avoid the special zombies. While killing them with a silenced gun will count, it's not worth the time.
If you ever end up in a bad predicament, just quit out of your current game and then select "Continue".
DON'T start a new game unless you want to have to wait till night again. Continue should keep the same in-game time period.
You should have the achievement app snapped while you do this, if progress doesn't go up then turn off the console and reboot the game.