From the walk in with the Joker to the first mutated henchman: the Holding Cells fights, Zsasz in Patient Pacification, the Decontamination rescue and every Riddler item these rooms allow without gadgets.
Decontamination: rescue both guards and the thug, clear the toxinQuest stepMissablePoint of no return
Location
Intensive Treatment · Decontamination – Past the window onto the chamber (the guards behind the glass can't be saved), grapple up to a higher ledge and crawl through the vent. Coming out, turn right and pull up the first guard; leap over to the neighbouring platform, then grapple onto the higher one and look left for the second; then glide down to the lower platform ahead for the thug, whom Batman knocks out. In Detective Mode, turn left and hit the fan control panel with a Batarang to blow the gas away.
Why you can lose it
Lost if one of the three men falls into the toxin and you then leave Decontamination: the room is never replayed on this save, so only a new game (the Hard run) gives another try.
Point of no return
Leaving Decontamination for the Transfer Loop (the room change writes a new checkpoint). If one of the two guards or the thug fell into the toxin, Leave No Man Behind is lost on this save; the Hard run is the next chance.
Summary
Pull two guards and a thug up before they fall into the Joker toxin, then clear the gas. Saving all three earns Leave No Man Behind.
Back on the surface after the sewers: snipers now hold Arkham North and Arkham East, and the locked-down Mansion is entered through a roof vent with the new Batclaw, up to Dr. Young's Office.
Riddle: Ra's al Ghul's bodyCollectibleMissablePoint of no return
Location
Arkham Mansion · Dr. Young's Office, mortuary wall – Back in the ceiling space, take the other vent route above the North Corridor and drop into Dr. Young's Office, where three thugs stand outside her inner room; knock the one with a gun out first. Then climb the stairs to the wall of morgue drawers: one is pulled out, a bagged body's feet showing. Scan the tag tied to its toe.
Why you can lose it
The body is gone on a later return to Dr. Young's Office, and the exact trigger isn't known: scan it before you leave the office on this first visit.
Point of no return
Leaving Dr. Young's Office for the West Wing Corridor on this first visit. The body at the mortuary wall is gone on a later return and the exact trigger isn't known, so the guide treats leaving the office as the deadline.
Summary
A Riddler riddle: the answer is the toe tag on Ra's al Ghul's body in Dr. Young's Office. It can be lost, so scan it on this first visit.
The last Chronicle in the Security Control Room, then the Joker's party at the Visitor Center (Party Pooper and Freeflow Combo 40 in one fight), the Throne Room, the final fight on the Penitentiary Roof and free roam after the credits.
Party Pooper: knock out all 20 party thugsHidden spoiler – activate to revealAchievementMissablePoint of no returnMajor spoiler
Location
Arkham West · Visitor Center – Back out of the Penitentiary, go to the Visitor Center front, the doors painted with the Joker's face, and take on the 4 thugs standing there. With all four down, go in by the smaller red-painted side entrance and knock out all 16 thugs in the hallway behind it before you touch the door at its far end. Read the next item before you go in: the hallway fight is your best Freeflow Combo 40 chance.
Why you can lose it
Lost once you go through the hallway's far door into the Visitor Room with any of the 20 still standing: there is no way back out until the credits, and the thugs are gone afterwards. Only the Hard run gives another try.
Point of no return
Going in by the red side entrance into the Visitor Center hallway (the 4 thugs outside may be out of reach once you are inside), and at the latest through the door at the far end of the hallway into the Visitor Room. From there the story runs on to the ending with no way back out, the checkpoint moves past the party, and the party thugs are gone after the credits. Party Pooper is then lost on this save; the Hard run is the next chance.
A missable trophy for knocking out every thug at the Joker's party, 4 outside the Visitor Center and 16 in its hallway, before going into the Visitor Room.
PC (Steam)
Before you leave the Penitentiary for the party, copy the save file (.sgd) somewhere safe: it is a way back if the fight goes wrong after the checkpoint has moved on.
A second, story-only playthrough on a new save at Hard for the last difficulty trophy, with a Hard note for every boss and second chances at the two missable trophies if run 1 lost them.
Hard run fallback: Leave No Man Behind (only if run 1 missed it)Quest stepMissablePoint of no returnNG+1
Location
Intensive Treatment · Decontamination – Reached as in run 1, in "Intensive Treatment: arrival", after Zsasz and the vents. Coming out of the vent, pull up the guard ahead of you, then the second guard one level up, then glide down for the thug on the lower platform; Detective Mode shows all three. Clear the gas with a Batarang to the fan control panel. When Leave No Man Behind pops here, also tick run 1's Decontamination step, so your 100% count is complete.
Why you can lose it
Lost if one of the three falls into the toxin and you then leave Decontamination: the room never comes back on this save, and this is the last run the guide plans.
Point of no return
Leaving Decontamination for the Transfer Loop on the Hard save. If any of the three men fell, Leave No Man Behind is lost on this save as well.
Hard run fallback: Party Pooper (only if run 1 missed it)Hidden spoiler – activate to revealQuest stepMissablePoint of no returnNG+1Major spoiler
Location
Arkham West · Visitor Center – From Arkham North, where the Ivy fight ends, follow the objective to the Visitor Center and play the party as in run 1, in "The finale" (this run skips that section's Chronicle). Start on the 4 thugs at the Joker-painted front doors, then go in by the smaller red side entrance and drop all 16 in the hallway before you touch the far door. When Party Pooper pops here, also tick run 1's Party Pooper item.
Why you can lose it
Lost once you go through the hallway's far door into the Visitor Room with any of the 20 still standing: there is no way back out before the credits, and this is the last run the guide plans.
Point of no return
Going in by the red side entrance into the Visitor Center hallway on the Hard save (the 4 thugs outside may be out of reach once you are inside), and at the latest through the door into the Visitor Room. The story then runs to the ending; any party thug still standing means Party Pooper is lost on this save as well.