Here is a guide on how to get the endings in Project Downfall.
Ending B: (80% sure) kill ali, leave some witnesses alive
Ending C: leave Harold jones jr, Pavloch and Alfred alive, do small time, in “old friends” kill them all and go back to where you started. You should get the ending.
Ending D: do “Call of Duty” and then go to work and do your daily tasks until Ali calls you to go to Arnie’s diner. accept ali’s offer and DON’T do your daily tasks, instead just go to the exit. go to the stairs in the train station and not the train, and you will go to the level “great timing”. comply with the Svoloch mobsters all the way and you should get the ending.
Ending E: take a bunch of pills and don’t go to arlovski. Do “liberator”. go to cloudbreak station and everything should be weird in the office. Finish the level and when you are back at your apartment, go to the elevator. You should then get the ending after a short cutscene.
Ending F: take a bunch of pills, in the “Rising High” level you should see a hallucination of Olga. kill her and then do the pill ending levels until you reach exodus. after you kill the enemies, there should be a giant fleshy hole to your left. Go in it and proceed with the level.
Ending G: Kill all your witnesses. (Ali, Burger King, etc.) finish small time and you should go to “old firends” with no-one there. Then you simply walk to the balcony. (this is not a pill ending, dont go way overboard)
Ending H: Do all the levels normally, finishing on small time. Easiest ending in the game.
Ending I: (90% sure) do call of duty, work until you get promoted to level 2. DON’T go to lunch with Ali. Then the Kyon’cha shows up in the exchange level, yada yada… do the levels and then do “the setup” when it appears. you should get to a level called answers or something and yeah you have level 2 access so you can do that.
Ending J: same as ending I, but do liberator instead of Call of Duty. You should get “The exchange” immediately after clearing liberator.
Ending K: (80% sure) go crazy on pills and right before you do “the interview” go to dr arlovski. Then the levels should play out. Not sure if you have to kill ali or witnesses.
Ending L: go crazy on pills. Kill Ali and all witnesses. do “The interview” and you should get the ending.