Serial Killer Achievement
Win 10 Ranked Matches in any Deathmatch mode
Just win 10 Ranked matches. You can choose between DM, species TDM and mixed species TDM. The easiest tactic is playing with a party consisting of 4 players. Three should play as Alien or Predator and the last one as the other species. If the 3 are good the single player can sneak some kills as most players tend to play with a team of 3 Predators and/or 1-2 Aliens and the Predators usually only hunt the species with the most members.