Metro Last Light

This is the default ending to the game. Ignoring beggars, not helping others, and killing people (and, yes, mutants) when you don't have to.

If you're trying for the Redemption achievement, you'll know if you made it at the end of the next-to-last chapter, Polis, by what your companion says to you.

If he says, "I'll see what I can do," you'll get Redemption.
If he says, "You're good, Artyom," you'll get this.

There aren't any places to lose points in the last two missions, so if you got Redemption, you're probably going to have to go back several chapters to see if you can change your ending. I would suggest going back as far as The Dead City and doing the following to make sure that you're sufficiently not-good.

Dead City: Don't find the 3 optional visions
Kill all the mutants you can find. Make sure especially to

Red Square: Kill every mutant. Kill all the snipers. During your "choice" at the end, just do nothing. (Some people say that this is all you need to do... probably, but Dead City is a short, quick level.)

The Garden: Don't go into the store in the big building; just follow the normal path.
Don't shoot the mutants off of the Bear after the fight.

Hope this helps!

Edit: some people have said that Dead City wasn't far enough back, but Depot was. Better to go back further than not far enough. Regardless, you shouldn't have to replay the whole game, just a portion.

C'es't la vie - Destroy D6.

This Achievement is won by earning the "bad" ending of the game. Simply kill every enemy you meet, including enemies you are warned away from attacking by NPC's, kill any helpless NPC's you encounter, and generally behave like a jerk, and you'll have it wrapped up handily.

Just going to add this, not a TRUE Guide here. I was playing through to get the "No Human Kills" achievement when I did this 1st off. I was doing great till I accidentally killed one of the 2 guys at the gate before you go on to challenge Pavel in the Red Square, so right at the end of the game sort of and I was quite pissed this let me say. So when I challenged Pavel I also needed the "Kill Pavel" achievement as well so I just let him die by doing nothing when he was held by the arms in the dream sequence as I figured I had screwed up my "No Human Kills" by killing that one guy. I finished game but decided to try and do it without killing any humans (just hid and only destroyed the Train Tank and the Last Flamethrower guy) to see if I could do it for my next play through seeing as i screwed up and killed that one guy. Well I was quite surprised by my ending

1) I blew up D6 at the end and got this Achievement (Yeah)
2) I got the "Kill No Humans" Achievement (CONFUSED Yeah)
3) I got the "True Spartan" for doing the last stand without dying. (Surprised Yeah)

So to blow up D6 I think you only have to Kill Pavel as you get the Revenge achievement and the Dark One does not learn about Forgiveness so I think He does not come to Help you out at the end and you blow up D6.

Not an official guide here, just giving an example of how I got. I might add that I guess the Red Square fight is a FORCED fight and killing humans here in allowed, saw some posts saying you couldn't kill anyone here. You decide what you want to take from my experience here.