In Episode 15, if you do not kill anyone besides Leo and sneak your way to where mental Pickman and Michael are, instead of saying "Here's some more of your victims", Leo Kasper will say "What? Have you turned over a new leaf?"
Make you way to the door where the guard tells you he will not let you in because you are not a familiar face. Turn around. Go off the stage. Climb up the steps on your left. Then, go up the stairs on that side. Move up the stairs until reaching the top. On the right side down the hallway is a case on the wall. Inside the case is an ax. Use the ax on a person or body. Executions immediately detach a head, where as hacking at a corpse requires a few swings. Pick up the head. Run back to the door and equip the head as a weapon. Go to the door and press [Action]. The guard will let you in.
Original Manhunt references
Some of the Bloodhounds(in "Broadcast Interrupted", "Most Wanted", and "Altered State") are wearing Ku Klux Klan hoods. This is a reference to the Skins from the original Manhunt, although they were more Neo-Nazi-like.
Some of the Bloodhounds have appearances nearly identical to the Wardogs in the original Manhunt. They are depicted in camouflage jackets, camouflage pants, camouflage hat and a rebel bandana. All of the Wardogs had camouflage, but some of them also had camouflage caps and plaid bandanas.
The executions for the Sickle are basically redone versions of the sickle executions from the original Manhunt, but in different order. The first execution is the same as the Violent execution in the original Manhunt. The Violent execution is the same as the first execution in the original Manhunt, plus an extra strike to the face. The third execution remains the same, and is just slightly higher on the victim's torso.
The "J.E.C. and Sons" construction sign on the assassination level is a reference to James Earl Cash, the Protagonist of the original Manhunt . This construction company is also in Grand Theft Auto: San Andreas.
Red Dead Revolver reference
In "Broadcast Interrupted", near the end of the level just before the parking garage will be a small television in the room overlooking the western (5 Past High Noon) stage. This television is directly to the left of the doorway which leads to the padlocked double door to the elevator. Walk up to it and turn it on. It will show a cinematic that depicts a rather poorly-made trailer for "5 Past High Noon". The cowboy shown is Red Harlow from Red Dead Revolver, another game developed by Rockstar. You will also hear the announcer say, and see a caption on the screen, the same first few words from the Cortexa subliminal video used on Daniel, shown fully in "Origins" (specifically, the words "Trust", "Duty", "Love", "Hate").
Release Therapy bonus level
After completing the game for the first time, you will unlock a bonus level called "Release Therapy". In this level, you play as Leo rather than Daniel and fight lots of fairly difficult enemies. After defeating the final Boss, you will get the bad ending. Like the "personality clash" ending, it is unclear what happens to Danny or Leo after these events.
Relive Scene option
Successfully complete the game. This option allows any level to be replayed, as well as the "Release Therapy" bonus level.
Pickman's erasing line "What Seest thou else in the dark backward abysm of time" is a reference to Shakespeare's The Tempest.
Silence Of The Lambs reference
In "Ritual Cleansing", get over the semi blocking the door to the archive storage building. Collect the crowbar by climbing some boxes next to the storage room which the crowbar is in. There will also be piles of boxes on the roof of it. Once you get the crowbar, open the gate and move toward the farthest files. There will be a light tan gate with a padlock on the other side. Turn right and open the large gate. Inside this garage you will see a green car with an American flag tarp over it. This is the car from the scene in Silence Of The Lambs where Clarice (Jodie Foster) is investigating a rental garage, and finds a head in a pickle jar in the back seat.
The Shining reference
When Leo says "Danny's not in here", it is similar to what Tommy the imaginary boy in Danny's tooth in The Shining says when he has gone into his psychic vision state.