The Forces of Decay
I play for fun rather than enter competitive gaming so I am not that bothered about codex legality provided both players have a fun game.
One way to play something different is to mix and match from different codices provided, and this is the key bit, one does not power play, i.e. cheat.
I have a Nurgle themed army that is drawn from the Chaos Space Marine and Daemon codices.
HQ’s
1. Lord Swyneflue the Mephitic: Nurgle Daemon Prince.
2. Gangrenic: Great Unclean One.
Elite
1. The Dreadnought Slimecutter: Chaos Dreadnought.
2. Beast of Nurgle.
Troops
1. The Putridity: Champion and Plague Marines.
2. Plaguebearers
Fast Attack :
1. Oh come on; did you expect any?
Heavy Support
1. Spitpuss: Plaguereaper (Nurgle Baneblade).
This makes up an approximately 1500 point army. The Plaguereaper is just there for laughs. I use a house rule that says that apocalypse templates are not used on normal-sized tables. The daemons must arrive from reserve using deep strike.
This army is brittle and unstable. Results vary wildly from game to game.