Brutal Guts

Easy Z but does require multiplayer matchmaking, however, you can do this in 8-player FFA on a H2A map: Zealot in Halo: The Master Chief Collection

Super easy O achievement, if you own the Halo 3: ODST DLC (or have Xbox Game Pass to install it): One-Way Ride in Halo: The Master Chief Collection

Super easy U achievement, if you own the Halo 3: ODST DLC (or have Xbox Game Pass to install it): Uplift Reserve in Halo: The Master Chief Collection

So basically, get 8 players for 8-player FFA on a H2A map (must set your preferred species to Elite in the in-game Settings prior to matchmaking), then win 10 times.

Follow that up with the Halo 3: ODST DLC mission called Uplift Reserve on Heroic difficulty but DO NOT use a health pack or any Covenant weapons.

I do have 2 consoles, 2 copies of the game, and 8 controllers if you need help with the Zealot achievement in MCC.

OK thanks man. I got your text too btw. Super hesitant to start MCC still due to the tanking it would do to my completion percentage, lol.