First off to get this you need to use the Chaos Lord. Beyond that you can use Heretics and any unit that can be given the mark of Khorne, such as Chaos Space Marines and Havoc's. You can also use Dreadnoughts and Predators as well as the Khorne Deamon units, Bloodletters and Blood Crushers. You can not use Mark of Tzeentch or Nurgle upgrades Plague Marines, or the Great Unclean one.
If you use a neutral unit, one without a mark and do not upgrade before the end of the game you will still get the achievement.