If you plan to get all 65 achievements for Halo 5, you better buckle up because some of the requirements are going to take some time to accomplish. Some of the achievements are simple and will come easy, others will have you at your wits end ready to pull your hair out. One that looks like it will be tough to finish:
Complete every Mission of the game on Legendary difficulty, by yourself.
Do be warned though, this list will contain spoilers and contains names that will be featured in game.