Halo 2: Complete a match on at least 8 different classic multiplayer maps.
This achievement can be obtained quickly through Custom Games on your own at any point during your time on the game. From the Main Menu, select the Multiplayer tab and head into a Halo 2 Classic Custom Game lobby. From here, go ahead and select the very first map available and then launch the match.
Once the match begins, pause the game and select “Quit.” This will count as a completed match on that particular map which means all you need to do is repeat this simple process on seven other Halo 2 classic maps. Once you have completed a match on eight different classic maps, this achievement will unlock. Just make sure you are choosing classic Halo 2 maps and not the six remastered maps!