Emergence Day, fourteen years before the first game.
First steps, core mechanics and introductory quests
Configure controls and familiarize yourself with basic mechanics before proceeding.
Advance through the main campaign while watching for cutoff points
Cross the climactic point of the main storyline to complete the game.
Side objectives that must be cleared prior to the story climax
Chapters close behind you. In Act 2, Chapter 2, Hold the Line, the gate to Charlie Squad and the hotel at the end of the chapter are two: pick up what is around before going through.
Each one has to be accepted when it is offered. Some you are pointed to; others you only find by following a firefight or a conversation, and some are tied to a moment in the chapter.
Some collectibles and Hard Cases only become reachable after a main objective. If one is on the map but out of reach, it is not missed yet: come back later in the chapter.
One collectible is only handed over when the campaign ends, so the count is not complete until you have finished Act 5.
Replay the chapter of the Hard Case.
They need all of the above as well as Insane; see the Achievement Roadmap for how the difficulty part reads.
Gathering remaining collectibles and securing 100% completion
Xbox Wire's official list has 54 worth 1,000G; Steam adds The Lucky Ones Died on E-Day at 0G for earning the rest: 55 here, though the guides count 53 to 55, as What We Know explains. Thirteen come with the story, five more need the campaign cleared — one in co-op, three on Insane — and most of the rest are Horde Siege and Versus grinds. The order is on the Achievement Roadmap.
The campaign's collectibles, act by act. A COG Omen sting plays when one is close, the War Journal shows which are still missing, and chapter select takes you back for any you passed. All of them: Memories From E-Day.
Yellow cases holding weapon mods and mod slots, which you fit at Supply Caches. A pop-up says when one is near, and some only open after a main objective. All of them: Relax. I'm the Map.
Optional jobs for the soldiers and civilians of Kalona, from Act 2, Chapter 2 on. You accept each one when it is offered, and they pay in weapon mods. All of them: Side Piece.