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I can't deside if Nurgle and Khorne make a good combo for an army list.
I'd run the fallowing and think that your input would be helpful.
Khorne Hero of a Juggernaut
2 units of 15 Nurgle Warriors with shields
1 unit of unmarked 20 marauders
2 units of 5 khorne kinights
4 Chaos Ogres with 2 hand weapons
The list runs between 2000 and 2250. The knights and the juggernaut run around the sides and the warriors and marauders pretty much go strait up the middle with the ogres helping out where ever.
The question is do I run all nurgle and lose the khorne mark?
Unfortunately the question at hand and the list are both slightly too vague for me to offer much in the way of useful criticism. Here goes nothing though!
I have found Khorne Knights very useful for running distraction/occasional mass murder duty. If you march the Orges and the Warriors up the middle and use the Knights as a kind of pincer, yes, I think that is an entirely valid tactic.