I have a few achievements missing from Halo Reach but I am unsure how to get them in multiplayer. The problem is getting into the game modes on the right map.
The achievements are.
Paper Beats Rock
Defiant: Assassinate a player that just exited Armor-Lock in a matchmade game.
Defiant: Be the last surviving uninfected player in a matchmade Infection game.
Anniversary: Infect 3 players in a single round in a matchmade Infection game.
Anniversary: Capture 10 skulls at once in a matchmade Headhunter game.
Can anyone help?