There is a trivia in the best ending that asks questions based on what happens on the other endings, so here are the endings you NEED to do before the best ending (you can do the other endings when you feel like it)

• Luigi solo ending

• Yoshi solo ending

• Worst ending (there will be a question on Mario.exe's real name, so to get that answer early in the game, I suggest you do this ending or you can check the description of this game to get the answer)