Warframe

No need to be invisible, can be done with any Warframe.

Mission: Cambria on Earth

This mission has loads of long ziplines every time, use a bow or other silent weapon, there are patrolling Grineer-soldiers in every area, plus there will be wild kubrows which spawn from kubrow dens, just keep shooting the dens and more kubrow will come out.

2022 edit. Solution seems to be outdated, so I'll add TG Airborne 88:s solution.

"My suggestion would lead to having a Loki frame. Have any bow, go to planet Mars, mission Kadesh. It's a defense type with infestation to kill.

Just wait for a bunch to gather around the pod, go invisible, jump on the zip line and get about 2-4 kills per time done."

Malva sector on Venus is a Dark Sector Excavation, level 10-20 and how I got this achievement. Unfortunately, with the starchart change, it is no longer an excavation but a survival. If it's the same map though, that should work well if you can go into a stealth mode. A potential substitute according to Geoffistopheles is Venus - Kiliken with level 5-7 Corpus, although not as good as infested.

I used Loki for the invisibility, and this map because one of the Corpus tilesets spawns you right next to several zip lines on a roof. That is one of the only tilesets in any mission that has native zip lines and is fairly easy to access.

The tileset spawn you want spawns you on a roof near some ziplines. If you don't get the roof spawn, abort the mission, and start it again. I got it 1st try, then 4th try doing this.

From there, just jump down off the roof, activate the Extractor, wait for it to die to the infested, then run through or around the building back to the ziplines. If you stand under them and press it will automatically put you onto the lower one if you're standing close enough!

So, get the Infested to follow you there, activate Invisibility, jump onto the zipline and kill the Infested with a silent weapon(I used Loki's mod Hushed Invisibility which makes weapons silent while invisible). Otherwise a bow would work well if it's strong enough.

The Infested will keep spawning, just lead them to the zip line if they aren't close enough, and it goes fast! I got all 30 in a couple minutes.

Note: I have Ivara, but she's at level 1, so I couldn't test out her ziplines. If you don't have Ivara, Loki works really well on this map! If you don't have Ivara OR Loki, Loki's invisibility unlocks sooner than Ivara's Prowl by a few levels.

My Loki Prime max speed build(Sprint speed 1.96):
My Loki Prime invisibility build(203% Power Duration):

I used Ivara for this. Very easy, because you can use her Dashwire arrow to create a zipline just about anywhere on the map. Get up on the zipline and use Prowl to go invisible. Even if the enemies are aware of your presence, once you go into Prowl, they become unaware without having to reset the alarm. Then use a Bow or any silenced weapon to get your kills. Pick a map on Earth, so everything is a 1-shot kill.

You can probably use Loki too, but you'll have to find a zipline somewhere on the map.

You can get this in a couple minutes if you have:

a) Loki or Iwara
b) a bow weapon
c) an ODD key (Orokin Derelict Defense - you can buy the key blueprint in the market and build it in the foundry)

I used Loki and the Rakta Cernos - ideally you set up your Loki/Iwara to stay invisible as long as possible and your bow to do max damage for one shot kills.

Load up the ODD mission and you'll see there is a zipline pretty close to the pod you're supposed to be defending. Now simply stand under the zipline, use Loki's Invisibility or Iwara's Prowl, hit to jump up onto the zipline and use your bow to kill all the infested enemies that will be swarming the pod. When your Invisibilty runs out simply jump down and rinse and repeat until you have your 30 stealth kills. Once the achievement pops either just abort the mission (which lets you keep your key) or play on and you will be able to extract every 5 waves.

Good luck Tenno.

For those without a Loki or Ivara and maybe not even having level 30 weapons there is a pretty straightforward way to get this done.

If you have a sentinel or kubrow, leave them behind.

I used an Excalibur and chose to go to Earth to find a nice low level mission with infinite enemies, or in other words, any mission that is not an exterminate. I don't recommend a defense mission for this as there is an extremely small map and even if you are on a line and they don't see you, they are in attack mode and chances of getting a stealth kill are much lower. There are several rooms that spawn on Earth in the low level sabotage mission on Mariana that can make this very simple.

Find a room with a zip line and hop on up. It didn't matter if I cleared that room first or not as I found that there would be at least a couple more that would randomly wander into that room. If I didn't see any enemies for about a minute I moved on to another room. On my second run I had a room where there were entrances on both ends and a zip line in the middle. This particular room is also the tile that you defend your kubrow when you first get it in the "Howl of the Kubrow" quest. In less than 30 minutes total I had my achievement. Of course this can vary depending on how the tiles fall for you.

A few tips are to always attempt a headshot. I know, head shots on Grineer are hit and miss as far as getting credit for them, but even if you don't one shot them and they become aware of you, there will usually only be the one or two enemies and after you take care of them the next few in the room will be unaware of your presence.

Don't sit on a line for two forevers waiting for one to wander in, if you don't get one in a minute or so move on.

There are several zip lines on the low level Earth missions to work with so even if you don't get all of your kills on one line you may have several opportunities on the same mission to get it done. I do believe that Earth offers the highest amount of zip lines to work with. If there is a place with more lines then chances are the enemies are higher level and have a better chance of surviving a headshot.

And if you get two enemies walking in at the same time try to take out the second one first. If you take out the first one then the second usually becomes aware of you and you tend to not get a stealth kill for the second.

Hope this helps. Happy hunting.