How to cheese the "Ouroboros" Achievement

The quickest and easiest way to beat the par time for the level "Infinity" is not to play the mission normally. Instead, you'll have to navigate into the campaign, select cross-game playlists, and play through the first three levels in the "Hogs, Jets, Tanks, and Mechs" playlist. If you want to beat the par times for those levels, the YouTube channel HaloCompletionist has good videos for each level's achievement. Regardless- once you beat those three levels, you'll want to play the last mission in the playlist which is "Infinity" from Halo 4. The reason you want to do it this way is because this playlist starts you in the latter half of the level, when you get to start driving vehicles. Despite this however, the game still thinks your time is for the overall level, so once you finish the level, it will think your completion time starting from getting the Scorpion is your time for the entire level. Because of this, getting the par time is a breeze. All you have to do when you start up the level is just play through it normally. Since the game started you half way through the level, getting the par time should be easy since you have 25 minutes to complete the remainder of the stage.