Middle-earth: Shadow of War

The 'Better Luck Next Time' achievement is one that doesn't have a set trigger to unlock and is completely random on when it could happen.

For an enemy to cheat death, they need to be of the captain class. When you kill them, sometimes they will seem dead in the nemesis menu and drop a reward like other captains but will actually have a small chance and remaining alive, even after your first fight. You will have the chance to run into them randomly or through the nemesis system where they will most of the time become stronger then when you previously fought. After you meet each-other again the achievement will unlock instantly.

Here is a video showcasing how such an encounter works.

Although there is no real "trigger" to this achievement. I found one way that seems to get the same Grunt to follow you around multiple cities.

1) Roll up, roll up, kill a captain, any captain will do.
2) Let a grunt kill you.
3) Go to the Avenge mission and instead of recruiting him, hit to shame him, lowering his level.
4) Find him on a new point on the map and kill him
5) He should turn up as an ambush either during a mission or as you walk around aimlessly.

I've done this a few times, the second time, I even shamed him a second time, this drove him mad and he followed me to Ambush me on my first visit to Gorgoroth, he proceeded to get himself killed by a Caragor. He then respawned again to get killed by a follower of mine.