Difficult Achievements you got by accident.

[Zhukov]

XCOM: Enemy Unknown - 'As a Scalpel'

You have to complete a terror mission keeping all your soldiers alive and, this is the hard part, keeping all civilians alive.

I still have no idea when or how I did it. It's pretty much entirely luck based, since civilians will generally start getting killed off all over the map before you've even left the LZ.

 

[Gethsemani_v1legacy]

XCOM: Enemy Unknown - 'As a Scalpel'

You have to complete a terror mission keeping all your soldiers alive and, this is the hard part, keeping all civilians alive.

I still have no idea when or how I did it. It's pretty much entirely luck based, since civilians will generally start getting killed off all over the map before you've even left the LZ.

This. I got it on my second or third terror mission when I wanted to try out an assault heavy squad line-up. I completed the terror mission on round 4 and got the achievement after some intense, but hilarious, shotgun action.

 

[Aeshi]

XCOM: Enemy Unknown - 'As a Scalpel'

You have to complete a terror mission keeping all your soldiers alive and, this is the hard part, keeping all civilians alive.

I still have no idea when or how I did it. It's pretty much entirely luck based, since civilians will generally start getting killed off all over the map before you've even left the LZ.

I'll third this. I got lucky and got a Terror Mission where the aliens both weren't that strong and bumped into me basically on the first turn.


I also got "Shotgun 101" from Payday 2 by accident. It requires you to achieve 101% or greater accuracy in a mission where you killed at least 50 enemies, and you can't use any weapons that aren't Shotguns.

 

[Batou667]

I think it's called "Two For One" or "Bombardier" in World of Tanks - you have to kill two enemy tanks with the same artillery shell, which is very tricky to plan for as near-death enemy players will rarely be nice enough to sit still right next to a low-health comrade, and placing Artillery shells is a numbers game at best due to the scatter and travel time.

Anyway, I managed to do that twice, both times just through normal play and without particularly looking out for it. Apparently it's considered the hardest achievement in the game though, so I'm glad to have it out of the way.