This game has a campaign mode and no multiplayer mode. The achievements are straight forward and the kill related ones are easy to grind. However, you will need at least two complete playthroughs and one further part playthrough to mop up the remaining level/character specific achievements.
Start the game on easy. Always try to go for the mission specific achievements as you go through the mission. You can of course replay the levels individually but why bother with another playthrough when you can easily mop up everything in one go. It also prevents you from doing these on the hard playthrough because they might prove difficult on later levels. You can change the difficulty in the base menues, so no need to start a new game after you finished the game on easy (this way you can keep all equipment you unlocked).
The game doesnt save until you reach a save point, so it record each kill you did with a weapon of choice until the game has been saved. Go for one weapon at a time, keep killing until you get the corresponding achievement, then switch weapons or change your loadout after the mission is done. There is a spot where you can grind these as well which i will mention later on.
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