-Estimated achievement difficulty: 6/10
-Offline: 37 (795)
-Online: 13 (205)
-Approximate amount of time to 1000: 30-40 hours
-Minimum number of playthroughs needed: 1
-Number of missable achievements: 12 (Cannibal, Fashionable, Roadkill, Ghandi, Romantic, Heart of Gold, Anti Air, Take a Look at the Sky, Obsessive Collector, Completionist, One With the Dark, Legendary Summoner)
-Glitched achievements: Multiplayer Tracking sometimes resets itself, and single player difficulty can as well.
The Darkness is a first-person shooter based on the comic book of the same name. It only requires one play of the main story, but there are quite a few missable achievements. There are two different collectibles needed that can be missed: darkling outfits and underworld letters. There are also a number of story-based achievements that can only be done at certain times that can also be missed. Also locate and make note of all the "weapon" achievements for using the various Darkness powers and work on those accordingly. They are technically missable, but you can load a checkpoint and kill the same guys over and over to knock them out quickly.
Step 1: Single Player
First things first, DO NOT play multiplayer at any time while working on your single player campaign. If you do, the difficulty will reset itself from Hard to Normal and you will not be able to get the Legendary Dark achievement.
Again, be sure to follow the collectibles guide for the letters anytime you enter the WWII-era "underworld" sections to finish off Obsessive Collector and Completionist (73/100 collectibles can be obtained through phone numbers, the remaining 27 require the letters), and be sure to grab all the Darkling outfits for Fashionable. Anytime you acquire a new Darkness power, use it until it is maxed out. Also be sure to eat the heart of anyone you kill, as 180 are required for One With the Dark and 300 are required for Cannibal, and summon a Darkling whenever you can as 50 are required for Legendary Summoner.
You're going to want to start playing on Hard right from the start. The beginning sections are by far the hardest, but once your Darkness powers manifest the game is a cakewalk. Right when the game starts you're going to be coming on a missable achievement Roadkill for killing the workers in the tunnels. If you don't get it by the time the car crashes, restart the game. After this you will be in a cemetary and find a bum in the bathroom where your Darkness powers manifest. Do not kill the bum! If you kill him, you will lose out on the Heart of Gold achievement. Toward the beginning of the game you will meet with your girlfriend in her apartment for Romantic. She will ask you to watch a movie and eventually fall asleep. Do not touch the controller during this section or you will miss this achievement. When you meet with Harry later on at his hideout, do not pull a gun or manifest your Darkness or you will lose the Ghandi achievement. Later on when escaping the Turkish Baths, be sure to bring down the helicopter with your Black Hole power for Anti Air. And finally, when on the mounted gun during the second instance of the "underworld" be sure to destroy at least six planes with said gun for Take a Look to the Sky.
Step 2: Multiplayer
Another little glitch in this game is that sometimes the multiplayer stats (games won) will reset itself to a lower number or even all the way back to zero. It is suggested that you try and do these in one sitting or no more than two-three sittings.
First knock out all the random achievements for killing streaks and near-death retaliation (Bullet Dodger requires 4 players) and then grab a friend (or 3) and do Capture the Flag matches (in a player match) for the 250 wins required for The Don. The other person can leave and do whatever since the games with auto-launch over and over, then you can switch when the other person needs wins.
x360a would like to thank The Pants Party for this Road Map