How to unlock every achievement, which ones you can miss, and the best order to get them all. Tick them off as you go.
25-35 hours
Time to 100%
7/10
Difficulty
2
Playthroughs
6
Missable achievements
1 collectible18 cumulative15 difficulty
Points of no return
Chapter 9: Shooting gallery in the USM Valor Armory becomes permanently inaccessible once the USM Valor explodes and sinks.
Chapter 9: Any logs, weapon upgrades, and nodes aboard the USM Valor become permanently inaccessible once you escape back to the Ishimura.
Chapter 11 shuttle departure in Hangar Bay: Leaving for Aegis VII locks out the entire USG Ishimura, making all unfinished side missions, logs, weapon upgrades, the Master Clearance terminal, and the Peng treasure permanently inaccessible for the rest of that playthrough.
Recommended order
Step 1
Playthrough 1 on Medium or Story difficulty using only the Plasma Cutter to unlock One Gun, while exploring thoroughly, gathering all weapon upgrades, collecting logs and nodes, and completing all three side missions (Scientific Methods, You Are Not Authorized, and Premeditated Malpractice).
In Chapter 9 aboard the USM Valor, destroy all shooting gallery targets in the Armory before advancing past the torpedo bay, and make sure to grab the Peng treasure in Chapter 11 inside Hangar Bay before departing the Ishimura.
Step 3
Finish Chapter 12 on Playthrough 1 to unlock the Level 6 Suit schematic and credit bonus for New Game Plus.
Step 4
Start New Game Plus on Impossible difficulty (or complete New Game Plus on Story to finish all weapon upgrades and gather the 12 Marker Fragments for the alternate ending, then do a separate Impossible run if preferred; however, doing Impossible on NG+ or a standalone run is required for Untouchable).
Collect all 12 Marker Fragments exclusively available in New Game Plus across the decks, place them on the shrine in Executive Quarters on the Crew Deck (Chapter 10), and complete the game to witness the alternate ending and unlock Reunion.