Originally Posted by Tonic24k
First off, you're going to choose one suit choice all the way through from the beginning. Also, despite the achievement guide's recommendation, keep the auto save feature ON. If it is disabled you will not be able to take advantage of starting a new game while keeping all of your earned stats. It's the only way the game will save at the ending credits for the method to work properly.
Once in chapter 3 you're gonna be looking out for these last few missions: Serve and Protect, which is where you defend the 3 blue gates with black widow and then defend the entrance door against the berserk (red) symbiotes. You will then meet up with MJ and Cage in Harlem. Once you've finished talking with them you will receive the mission, Go To Church. After you finish up with this mission you will be prompted to Go Back To Harlem. Here is where you want to manually save the game in case you miss the next opportunity which is very easily bypassed. The reason is because once you talk with MJ and Cage again in the Harlem park, dialogue carries you to the next task and all the way through the Symbiote Black Cat fight. After this conversation you will proceed into the mission, Get Outta Town. Once you finish up with this convoy mission this is the one point where you get to save your game JUST before the Black Cat battle. You cannot save during a mission so immediately after you complete the convoy mission you will go to the Mission Complete screen and be given the option to "Continue" or "Upgrade". Go to "Upgrade" and hit RT until you're at the options menu and save here. This will put you exactly where you need to be when you return to change your suit path for one of the other endings. Now you will automatically be in the mission, Find Black Cat. Find her, defeat her, and then choose your suite choice just as you have been the entire game. You will go directly into another boss fight and then into the final battle. After this you will have one last suite choice and again, you will choose the same thing you have been.
Upon completion of the game and receiving an achievement for one of the endings, you will load up your save file from just after the convoy mission. This will take you right back into finding Black Cat. Once you defeat her this time, make the opposite suite choice and again after the last fight. For example, if you've been choosing the red suite choices all game, you would then choose the black suite after the Black Cat fight and the black suite again after the last boss. You will then receive another ending and it's corresponding achievement.
Now, for continuing your game with all your upgrades and collectibles you will watch the credits through after you beat the game and once back at the Main Menu you will select "Continue". This will take you right back to watching the credits again. Once they're over with for the second time, select "Continue" again and you will be at the opening scene of the game with everything from the previous play-through. This time, of course, you're going to be making the opposite suit choices.
All Red suit choices = Spider-Man & Mary Jane ending
All Red suit choices except the last 2 = Hero ending
All Black suite choices = Spider-Man & Black Cat ending
All Black suite choices except the last 2 = Antihero ending
Hopefully you completed 60 optional missions on your first run. Going through the game and completely neglecting these makes it go by SO much faster. I think i got to Chapter 3 in about an hour.
Well, I hope this clarifies how to get the ending achievements. I know the topic is scattered on this forum. So, by consolidating the information and adding some detail, I hope it makes it easier to get through and achieve the 1000 gs. If anyone has any questions or needs additional help please feel free to ask.