To see the full effect of how manipulating Blackreef's loop can impact things in Deatloop, one of the best puzzles is the Pact of Smoke door puzzle. Here's how to solve this tricky, multi-loop conundrum.
Deathloop Pact of the Smoke guide
To start, you'll need to head to the Smoking Contest near Colt's apartment in Updaam. The core of this puzzle is a locked door that requires three codes to open. Prepare for a fairly long haul on this one, as you'll have to visit three different locations on Blackreef across three different loops to get all the necessary door codes. It's also important to note that numeric codes are randomized across playthroughs in Deathloop, so your solution is probably going to be more or less unique.
To get going on gathering codes, you'll actually need to take a bit of a detour first. Start at the window in Colt's apartment to the right of the library and turn around. Look up the metal stairs to find either a door or open window that you can use to access the next room over. Here you'll find a smoking contest machine, and several notes/clues around the room about what's going on. Apparently one of the Eternalists is planning the ol' switcheroo to kill the others and keep the room for themselves.
Follow the pipes underneath the smoking contest machine to the other machine they're connected to. If you sabotage this machine, it will switch which pipe is safe to smoke, which determines both which Eternalists live and which codes for the door you're able to collect. You'll also have to use it once you've got all three codes.But, for now you're going to want to leave the contest machine alone, we just needed to find it and get the skinny on what the Eternalists are up to.
Return to Updaam in the afternoon and head back to the smoking contest room. Here you'll find new notes and an audio log from the deadly prankster, which give you your next clue. Then, go back to the room with the pipes in Updaam during the morning and push the button on the machine you found until the light lines up with the red pipe. Now you need to exit the level.
Next you'll need to go to Karl's Bay in the afternoon. Turn left when you leave Colt's tunnels and follow the road that goes past the Forever Young mural. Go down the stairs you come upon and open the door on your right. You'll find the next door code you need inside this building. Once you have it, leave the level.
Go back to Updaam in the morning and set the light in the pipe room to line up with the blue pipe this time. Return to Karl's Bay in the afternoon and follow the same path, but instead of taking the stairs at the end of the road, turn to the right around the corner where Shoot Them All is written. There will be a rooftop in front of you, cross it. Turn around from where you land and enter the building called Best of Blackreef to find the last note and code. Return to Updaam at any time of day to claim your prize.
For more Deathloop features and guides, check out our game hub.