One of the most talked about units in the new codex are Chaos Cultists. They're cheap, they're going to perish quickly, and there's potentially lots of them per unit.
And because they're just a little bit on the not so brilliant side, they could probably do with something to help them with their fear given their base leadership is 7 (or 8 on the champion). To be fair, orks are also cheap, but taken in large numbers, orks don't fear much. Tyranid gaunts are also cheap: but they get around things by having a hive mind to guide their actions. With chaos cultists, I think some fearlessness is the key to their role: we want them to bog down the enemy for a couple of turns. Let's say 2 combat turns. Beyond that, they're simply going to perish -- but that's the point. By the time those two turns have rolled around, we should have our other units in place, or taking care of things. The obvious thing is to run the chaos cultists with a dark apostle, or other HQ. Or just have done with it and turn them in to plague zombies via Typhus. Or maybe we could just take a large blob of cultists and hang back, hunkered down in cover and around a corner (avoiding line of sight) such that they simply sit on an objective all game long.
Let's have a look at a few alternatives.
35 Chaos Cultists, Mark of Nurgle (220 points)
Hang back, go to ground and sit on an objective away from line of sights. Stay put. Add a few heavy stubbers for fun if there's any points spare in the army.
35 Chaos Cultists, Mark of Tzeentch (185 points)
Cheap and get a 6+ invulnerable save when charging across the battlefield to engage enemies in combat. They're not going to survive long, but they'll survive fractionally longer with some good rolling. The 6+ save could be a nuisance factor that is needed. But perhaps only for those of you with lots of practised rolling. The Nurgle Mark (above) is arguably better in the long term. Perhaps implement a unit of 10 instead?
35 Chaos Cultists, 32 Autoguns, 3 Flamers (197 points)
Run with a fearless character and charge forward, shooting as you go. Use to seek out an objective on the opposite side of the field, or hang slightly back for a little cover fire.
35 Chaos Cultists, 3 Flamers, Mark of Khorne (235 points)
Use with a Khorne character, charge forward and engage enemy units for a maximum of two turns. Hopefully some back up will arrive by then? Swap out the Mark of Khorne for Mark of Slaanesh to create a 200 points unit that strikes at the same initiative step as Space Marines - might be useful?
35 Plague Zombies (150 points)
Typhus turns 35 Chaos Cultists in to Plague Zombies for the glory of Nurgle! This unit is the real business: fearless, feel no pain, and a little shambling thanks to slow and purposeful. Use to do what you like! Shamble forward and hold an enemy in combat for 2 turns as required. Sit on any objective you like. Take multiple units and still have points to spare for important support units and plague marines? Place Typhus in the middle and shamble toward melee?