Here is the list I used vs. the Ork horde.
The cultists and mutants melted away in the face of the big mobs, but the support options managed to take out smaller formations when used in combination. I was a little light on AA, but the Altar managed to knock out a Landa with a crit, which was a game-changer. The Contagion Towers being able to garrison is big, and they did
some damage, but they're better as a deterrent to units rushing up through their line of sight. The tough part with them is how fragile they are and how quickly they become ineffective with blast markers.
Overall, I still feel this list is a challenge with the 1:1 coven to support ratio you have to stick to, but it
can win games. The tough part is justifying units like demons, zombies, and Nurgle-specific, thematic units when the cost is so high compared with other awesome options like Leman Russ, Rough Riders, and Artillery.
I guess for league games I'd stick with lists close to the below, but for other games, I'd pack in the demons and zombies.
Doomed Legion, 3000 POINTS
Lost And The Damned (NetEA Army Compendium v20120208)
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STIGMATUS COVEN [225]
(Chaos Undivided), Chaos Marine Aspiring Champion, 11 Cultists, Traitor Fire Support
STIGMATUS COVEN [350]
(Chaos Undivided), 11 Cultists, Chaos Marine Aspiring Champion, 6 Chimera
STIGMATUS COVEN [350]
(Chaos Undivided), 11 Mutants, Chaos Marine Aspiring Champion, Chaos Altar
STIGMATUS COVEN [250]
(Chaos Undivided), Chaos Marine Aspiring Champion, 11 Mutants, Traitor Hydra
STIGMATUS COVEN [250]
(Chaos Undivided), 11 Mutants, Chaos Marine Aspiring Champion, Traitor Hydra
ARMOURED COMPANY [400]
6 Leman Russ
ARTILLERY BATTERY [325]
4 Basilisks
ARMOURED COMPANY [400]
6 Leman Russ
ROUGH RIDER PLATOON [150]
6 Rough Riders
NURGLE CONTAGION TOWERS [300]
4 Contagion Towers