First off to get this you need to use the Plague Champion. Beyond that you can use Heretics and any unit that can be given the mark of Nurgle, which at the moment is just the Predator. You can also use Plague Marines, and the Great Unclean one. You can not use Mark of Tzeentch or Khorne, Bloodletters or Blood Crushers
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.
This one is harder to get without boosting than the others, as you have a lot less options in Tier one. However if you use you shrines well to heal your units it's not too hard. This one would be easier to get in a team game as your team mates can make up for your limited unit choice and you can support them with your shrines.