The Invincible

At the bottom of condor towards the end of the game, move up in the elevator to the next floor and enter the medical bay, go straight ahead through to the Lobby at the very back and then take a right into Block H. Follow Block H to the very end and into the Hibernation Chamber room, inside will be the Keycard on the nearside left table and the Syringe on the far left table next to the window

After collecting the syringe etc head to the top floor and then follow the dialogue below:

At the bridge go through all the dialogue with Rohytra selecting whichever you want, ideally being against the bombs until you come to the Necroevolution theory. DO NOT choose the 'Necroevolution theory [discussion]', instead select 'There's no point speculating'.
Now when Novik asks if you agree about them being invincible select 'I fully agree. We shouldn't attack'
Rohytra will ask what else we can do if not attack, select 'Evacuate from here'
Rohytra will end the discussion and Yasna will say he won't stand down so for the next dialogue select 'I'm sorry I can't let you do it' and then click on Rohytras neck to inject the syringe and gain this achievement.

If you need more help with this you can follow my video guide below which will start at this ending/achievement:

Major spoilers, of course.


The achievement is about one of the possible outcomes in the final scene, the Condor deck.
First of all, i think you must have taken the narcotic syringe from the medical wing while ascending the Condor, like I did.
Then I'm afraid i do not have a guranteed sequence of the answers you have to input, but basically you have to talk Rohytra out of nuking the planet, but without being able to convince him: explain to him that the Cloud is non-sentient and that nuking it would do any/little good, but choose not to go into details when explaining the Cloud evolution.

When Rohytra is ready and willing to fire the nukes anyway, you have to choose the dialog option "i cannot let him do this" (or something similar), then get close to him and you'll have an "active point" to interact with. The achievement unlocks as soon as you put him to sleep using the syringe.

Note that once you finish the game you can then choose the "Continue" option in order to experiment with this and other different outcomes of the final scene: the last checkpoint takes you back at the beginning of the scene.