Here we are then, the 3 main endings which WOULD normally require you to play through it 3 times.
But with this little trick (Thanks to NoHeroes94) this is easily done in 1 playthrough.
When your outside Satans for the last time, it will autosave, so you should now completely quit the game.
Press your guide button, highlight Afterparty, Press
and quit out.
Reload back in, go through and do the 1 ending.. AS SOON AS THE FIRST ACHIEVEMENT unlocks, IMMEDIATELY go straight to your xbox dashboard WITHOUT quitting out of the game.
From there, go to My Game and Apps, highlight Afterparty, Press Start, down to Manage Game and Add ons, then down to Saved Data.
Click on your Gamertag, then IMPORTANT - Delete Local (Or Console) save ONLY!
DO NOT delete from everywhere as you will need to start the game again!
Once you have done that, reload back in, and you should be outside satans ready to do ending 2!
Go to 1:55:20 in my Part 2 video to see exactly how its done so you dont miss out.
Hope this helps.
Part 1
Part 2