The Marine Corps Gives Its Regards Achievement in Halo: The Master Chief Collection

Before anything, make sure to turn on "Scoring HUD" in the Campaign Lobby before starting a mission. This will help you keep track of your score during your mission playthroughs. In order to achieve the Par Score on all eight missions with Halo 3: ODST's Campaign, you will want to take four things into account. 

First, it is in my experience that most missions, when played on Legendary, did not require the activation of any skulls in order to reach a mission’s Par Score. The only mission that really needed skull activation and difficulty tweaking was Coastal Highway, which was set to Heroic with the Famine, Thunderstorm, and Tough Luck skulls. Secondly, Par Scores can be obtained in Co-Op play, so playing with another player or two will definitely help here. Thirdly, you will want to try completing the mission as quickly as possible (finishing under Par Time will give a x3 multiplier to your final score) while still killing everything on the battlefield via headshots and multikills; do leave anyone alive. Lastly, if you do happen to run over Par Time, try picking up the pace as the time multiplier will begin to reduce significantly!

You can use the checklist below for a reference on each mission’s Par Score:

• Tayari Plaza - 8,000 Points
• Uplift Reserve – 14,000 Points
• Kizingo Boulevard – 18,000 Points
• ONI Alpha Site – 16,000 Points
• NMPD HQ – 40,000 Points
• Kikowani Station – 42,000 Points
• Data Hive – 8,000 Points
• Coastal Highway – 90,000 Points

Once you beat the Par Score for all eight missions, this achievement will unlock.