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So far I have 3 knights of chaos regiments, a hellcannon, 2 chaos warrior regiments, and a lord of chaos....I am wondering if i should give them all a mark of nurgle and how I can expand on this army... please comment
I have a similar large force of mortals, and it looks like you should try a complete Undivided Horde so that you can mix and match your marks. Here are a few points I've picked up over the last few years that have served me well. They aren't perfect but are points to be noted and might make you look at the army book in a different way. I always find it helps to get someone else's view on things.
Hellcannon are great fun and like 40k dreadnoughts can be left to a flank where they will cause all sorts of upsets, leaving your small handful of remaining troops to mass together on the other side of the battlefield for saftety.
How many models in your knights units? I find five is enough as they're expensive in points and cash terms, and five knights do massive damage when they contact. They also survive longer in subsequent rounds of combat.
You will need light cavalry such as Marauder horse (with missile weapons as well as spears) and plenty of Hounds. These are cheap and essential as flank guards for your Knights. They will prevent your Knights from being rushed in the flank or by flyers, and can be used to flank enemy units the knights charge against. Knights move only slowly and can be prevented from marching by enemy light cav, but these can be driven away by missile-carrying Marauder light cavalry.
You should also think about Marauder foot to screen your Warriors (which suffer from the same problems as Knights-hard hitting but slow moving). You can also use Marauder foot as cannon fodder with a unit of warriors advancing behind them towards an enemy missile line (such as Empire). They're cheap in points, get a variety of weapons for several different tasks and are average enough not to cry over when they get wasted.
Another extra you can try are Furies. These cheap flyers can be used to take on enemy skirmishers and war machines as well as wizards and weak characters.
Chaos characters are also expensive, and like High Elves they do plenty of damage if used correctly. They can take on enemy characters and small units with impunity, however they aren't the centrepiece of the army. Sit your Lord on a Dragon or a mount and he moves fast enough not to be caught and can hit hard. Sorcerers are also powerful and not too vulnerable, however characters are expensive in points and only three powerful characters can use points better spent on two big unit of Marauders or several units of Hounds and Marauder horse. You could even exchange them for extra marks to give your units that supercharge they often need.
Finally, Chaos armies suffer from high points, low numbers and a glaring lack of missiles, unless you choose a Tzeentch theme. Then you get even fewer models as the mark of Tzeentch is expensive. You do however get a lot of magic missiles which can really hurt high T enemies like Dwarves (I smashed a mate's Dwarf army using 14 casting dice per turn).
There's something to be going on with. I hope it helps.
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